I've been using DNA testing to supplement my genealogical research and have made the rather startling discovery that the man whom I knew as my paternal grandfather was not in fact my father's biological father.

I first tested myself and my father on 23andme, with the expected result that my father was my biological father. I then tested my paternal grandmother, again with the expected result that she was my father's biological mother. However, when I started exploring my father's non-maternal matches, I could not tie any of them into my grandfather's side of my tree. This was when I started suspecting a non-paternal event of some type.

I recently became confident in my suspicions when my cousin (my father's niece) uploaded her AncestryDNA results to gedmatch. She matched as expected to my father's maternal phasing, but not at all to his paternal phasing. Additionally, she matched strongly to a third cousin on my (non-biological) grandfather's side of the family, so I think I can rule out another non-paternal event in her ancestry.

By researching the trees of some of the genetic matches to my father and finding crossover, I believe I have a good theory on who his biological father might actually be.

Both non-biological and potential biological grandfathers are deceased.

I believe my father has the right to know that his biological father is not the man he knew as his father, but how do I tell him? Do I tell him privately or with the rest of my family present? Do I prepare a presentation to try to prove it if he is resistant to the idea? Do I tell him my theory on who I believe to be his biological father? Do I contact the biological father's other family? Also, my paternal grandmother is still alive but suffering from dementia - do I bring this up with her, especially assuming it was a secret she may never have wanted to be revealed?


My father's father was not his biological father. How do I approach bringing this up with my family?

  • 15
    Must you tell your father???
    – RonJohn
    Commented Nov 28, 2017 at 20:30
  • 10
    why would you??
    – user4548
    Commented Nov 28, 2017 at 21:55
  • 1
    You are asking too many questions. Please edit your question to the question that most bothers you, which I suspect is "What is the best way to tell my father his father was not his father -- or should I keep mum?"
    – user1760
    Commented Nov 28, 2017 at 22:18
  • 9
    Please don't use comments to weigh in on whether or not the OP should do this. I've removed several and I edited such a thing out of another.
    – Catija
    Commented Nov 29, 2017 at 0:02
  • 1
    Have you considered contacting a genetic counselor? Whether you do or you don't tell him, the implications of this are quite significant either way.
    – faustus
    Commented Jun 21, 2018 at 3:40

7 Answers 7


People tend to leap to "infidelity" to explain this sort of situation, and it's certainly a common reason, but there are several other reasons why a woman might have a child whose DNA doesn't match her husband's. For example:

  1. Misleading DNA results: see e.g. the Lydia Fairchild case. It's hard to know how common such errors are, since most cases of chimerism probably go undetected.
  2. Husband was infertile, and they agreed to use a sperm donor (whether via old- or new-fashioned methods).
  3. Rape.

If the true explanation in your case is #1, it will be almost impossible to confirm that and hard to explain to family members who have a simplified understanding of how DNA works - you may end up damaging the reputation of somebody who is entirely innocent.

If it's #2 or #3, dragging it out in the open is likely to traumatise everybody involved for no tangible benefit. Most people are relatively relaxed about surrogacy-type arrangements these days, but for older generations that can still be a massive secret.

Something else to consider...

I then tested my paternal grandmother, again with the expected result that she was my father's biological mother.


my paternal grandmother is still alive but suffering from dementia

Did you obtain your grandmother's informed consent before testing her DNA?

Considering her dementia, was she capable of understanding the possible implications of DNA testing, as required to give informed consent?

If the answer to either of those is "no", you should seriously consider the ethical (and perhaps legal?) implications of releasing any information that rests on her test results, especially where that information could be harmful to her.

If she did understand that DNA testing can reveal information about parentage - and consented to it nevertheless - then perhaps she didn't believe she had anything to hide, which might be relevant to how you interpret this situation.

If it were me, I'd let it rest. I doubt it's going to do anybody any good to air this; if you do decide you need to tell your father, definitely do it in private.

  • 4
    I appreciate this answer because it provides logical alternatives other than the most upsetting one. I had a friend who found out in his mid 20s that his 'father' was not his biological one, because he had been infertile. His parents used a sperm donor instead, and had no intention of ever informing their children. To this day, he knows but his sister does not. It might be shocking information, but it's not always the worst case scenario.
    – Jess K.
    Commented Nov 29, 2017 at 16:10
  • I also am glad that you brought up the alternative circumstances of paternity. I had considered points two and three (which I would consider much more upsetting than infidelity), but I hadn't considered chimerism. I'm not sure whether this applies here but seems worth researching further.
    – Blamking
    Commented Nov 29, 2017 at 16:23

The earlier answer by @Geoffrey Brent is technically absolutely correct. May I only add from the interpersonal aspect (pardon my being so frank, but the situation calls for it) that it would be highly unethical of you to go ahead on your own initiative and break any such unsolicited life-changing information to your father, and probably very hurtful as well.

I believe my father has the right to know that his biological father is not the man he knew as his father.

That is a unilateral and potentially dangerous assumption, which you can validly make only if your father comes to know of your research and explicitly asks you about his biological parentage.


How can you be sure your father wants to know?

So don't do it. That is the only honest answer I can give you (and in good conscience could not avoid posting, in case you hadn't thought of this aspect) although you asked "how to do it."

Parentage is a very serious and very sensitive matter, and your father will not thank you for giving him this huge psychological shock which can change his life, affect his whole self-image and make him a very unhappy person.

Maybe you feel the need to unburden yourself of this secret? But that is unfortunately what can happen if you go testing your family's DNA, and possibly without their legally valid consent as noted by @Geoffrey Brent. Please consider the consequences. You cannot tell anybody without risking your father finding out, and it could seriously damage your personal relationship with your father.

If your father asks you point-blank and convinces you that he really wants to know about his biological parentage, then you might consider telling him, but strictly in private with nobody else present.

Otherwise keep it to yourself, your father doesn't need to know.

  • 2
    Otherwise keep it to yourself, your father doesn't need to know -- this....sometimes keeping your mouth shut is the right and hardest thing to do.
    – user1856
    Commented Nov 29, 2017 at 16:20
  • 2
    "sometimes keeping your mouth shut is the (...) hardest thing to do" __ So true @IamNotListening! Commented Nov 29, 2017 at 18:02
  • 5
    Also, how are we sure that the father doesn't already know? Just because he didn't tell his daughter doesn't mean he is unaware. Commented Nov 29, 2017 at 20:27
  • 1
    Yes indeed @Childishforlife. These are matters of the utmost delicacy and seriousness that won't withstand unsolicited interventions. 'Pandora's box' and 'Hornet's nest' are terms that come to mind. As one other answer rightly pointed out, no good is likely to come out of this action. Commented Nov 29, 2017 at 20:35
  • 3
    The new information might have been a bad surprise for the grandfather as well. Imagine the grandfather is a millionaire and alive - that information could cost your father his inheritance. Even if dead, if your father inherited lots of money from not-really-his-dad then the grandad's nephew might very well sue to get that inheritance.
    – gnasher729
    Commented Jun 14, 2018 at 20:28

There seems to be no way to tell him but the direct approach. Your grandmother's dementia makes it perhaps a bad idea to ask her. What about your mother - could you speak to her about it? Remember you may only be discovering something they already know about - if your father has confided in anyone wouldn't it be your mother? She may know what best to do.

Having said this, it does seem to me (although I'm no expert) that your evidence is only circumstantial. You don't have your grandfather's DNA. You assume that the disparity between your father and his other paternal relatives means your dad is the one not related to his father - but could it not be the other relatives you tested who were not related?

There are lots of arguments for and against following up your theory. The decision is yours, but obviously with your grandfather already deceased the window for discovering the truth and anyone that wishes to act on it is closing with the passing of time. It is possible your father could take the 'news' badly - it is also possible that it may explain things that have troubled him his entire life but never spoken of. There may be something important in his 'real' family's medical history that could save his life.

  • 5
    Thank you for bringing up medical history - most of the other answers seem to conclude that there is nothing to gain from bringing this up, but this is a valid counter-example.
    – Blamking
    Commented Nov 29, 2017 at 16:17
  • "It is possible your father could take the 'news' badly - it is also possible that it may explain things that have troubled him his entire life but never spoken of." For this reason plus the fact that I would want to know if it were me, I would tell my father. Alone, I'd approach it from the "Isn't science interesting? Look what this test shows..." with no pressure in my voice. I'd monitor his response and go from there. After that, no need to bring it up. I know it's hard because you have a lot of questions. Whatever route you choose, choose the path that honors your father the most.
    – Laura
    Commented Jun 19, 2018 at 20:40

I respect your decision to tell your father. Treating others as you would like to be treated is really the primary lesson from this stack exchange; I assume that if someone knew information about your paternity, you'd appreciate being informed.

Carry that principle further. How would you like to be informed of this information, if it was to be revealed to you? In public? In front of a gathering of family? I suspect not.

My thought is that you broach this confidentially, making sure that you put it in the context that it was an inadvertent side effect of other research you were doing. Give him the facts as you know them, and then make sure he understands that you are letting him decide how to interpret them and how to proceed. If he rejects it, or needs time to process it, don't make him feel like you are putting pressure on him. Let him know that you will keep this in confidence; in fact, I would tell him that you consider the matter closed, unless he wants to bring it up in the future.



I'd suggest you talk around the subject first. See what your dad wants. Tell him you're interested in family information you might find thru DNA research. You could say, "Some of this could be uncomfortable or unsettling," and add an open ended question like, "Is that something you'd be interested in?" or "If I find anything like that, would you want to know?" and just wait.

Probably a moot point after all this time, but.... One of my professors in med school told the story of a deathly ill young man who had been admitted to the hospital. He knew he was really sick. A CBC (blood count/analysis) told the diagnosis within hours--acute myelogenous leukemia, back in the day when there was no good treatment, and ~100% death rate within weeks.
When the prof walked in the room, the man shouted, "Don't tell me I have leukemia!!" --Showing of course that he knew, but didn't want to be hit with the word and the terrible associations. Sometimes people know, but they don't want to be confronted with knowing.

From experience giving bad/difficult/uncomfortable news, I'd suggest you talk around the subject first. See what your dad wants.

Tell him you've done (or planning to do?) DNA testing and you're curious to find out about relatives, and mention that people have discovered relatives they didn't know about, children out of wedlock or switched at birth, secret marriages, and all sorts of unexpected family history.

Then you could say, "Some of this could be uncomfortable or unsettling," and add an open ended question like, "Is that something you'd be interested in?" or "If I find anything like that, would you want to know?" and just wait.

?Tell us how this works out?




Psychology Today

5 Ways to Deliver Bad News With a Minimum of Pain

New research reveals why it's so hard, and a path to making it easier.

That most people have difficulty communicating bad news is reflected in what’s called the MUM effect (“keeping mum about undesirable messages”). In research on the MUM effect, Hope College’s Jason Dibble and colleagues (2015) define bad news as "a message communicating information that is previously unknown to the receiver, is anticipated to be personally relevant to the receiver, and is perceived by the delivery agent to be negatively valenced by the receiver”


From these studies, it seems that there is no one best way to convey bad news, but these 5 principles should provide some guidance:

1 Tell at least part of the truth if you think the person needs to hear it. Whether it’s a bad health prognosis or the need to let an employee you’re firing know how to avoid repeating the trouble in the future, there are situations when you can provide help to the person receiving the negative message.

2 Sugarcoat it if you think the person can’t handle it. (“It’s me not you.”) It may take you a while to frame the right way to create a positive spin, but it will be worth the investment, particularly if the individual seems vulnerable or fragile.

3 Follow the principles of politeness theory. It’s important for you to help the recipient save face when the bad news involves a potential threat to their self-esteem. You may have to develop a cover story in order to preserve the person’s reputation to the outside world, even if you and the other person know the actual reasons behind your decision.

4 Take your time to prepare your message. There is more effortful cognitive processing involved in presenting people with bad news. Make sure you consider carefully the meaning and possible interpretations of your words. Once certain words are said they’re impossible to take back, so don’t rush into an explanation just for the sake of getting it over with.

5 Rely on others to help you. Without blaming others or delegating the dirty work, keep in mind the Igier study’s findings and consider bringing relevant other players into the picture. It may be the other members of a work team, an individual’s family, or even someone impartial to provide moral support to both you and the recipient.

The good thing about PT is how it presents research info in an informal, conversational style.

And now a little drink from the fire hose....

Masthead J Educ and Health Promotion

Medical training for communication of bad news: A literature review ...

guidelines divide the interaction basically into three steps:

(a) Preparation for communication of the news, establishing personal contact, and the degree of knowledge of the patients regarding the diagnosis and extent of the information they want to receive

(b) the information itself, with appropriate language and rhythm, and

(c) an empathic response to the reaction of the patient. Besides guiding the verbal content that should be expressed, the guidelines take into account the nonverbal impact of the quality of communication.

Masthead CA: A Cancer Journal for Clinicians

SPIKES: A Framework for Prognostic Discussions

The SPIKES protocol provides an organized framework for prognostic conversations, and indeed for many other examples of “bad news” conversations. In addition, in 2007 the Journal of the Australian Medical Association published the Clinical Practice Guidelines for Communicating Prognosis and End‐of‐life Issues with Adults in the Advanced Stages of Life‐Limiting Illness and Their Caregivers, which has expanded communication guidelines similar to those proposed in SPIKES, but also includes recommendations for addressing the issue of hope.

Recommendations for prognostic disclosure, based on studies of patient preferences, guidelines, and expert opinion are described below, following the SPIKES format.

Table 4. SPIKES: Six‐Step Protocol for Breaking Bad News


S: Setting Prepare yourself emotionally for the anticipated conversation. Obtain all relevant laboratory, pathology, and radiologic data, and speak with collaborating providers. Formulate your prognostic estimate. Include pertinent persons such as the healthcare proxy and family or friends; also consider inviting collaborating providers. Prepare the physical environment. (Are there enough chairs, and are tissues available?) Limit interruptions.

P: Perception Find out what the patient understands about his or her disease and situation.  

''What is your understanding of your health situation?''

the current state of your cancer?''   

the reason we ordered the recent PET/CT?''   

your progress during this hospitalization?''   

your biggest concern at the moment?''

I: Invitation/Information Ask the patient what kind of information they would like to receive. “Are you the type of person who likes to know details or numbers, or do you prefer more general information?” “How much would you like to know?”

K: Knowledge Provide information in clear, nonmedical language targeted to the patient's educational level and information preferences. Acknowledge limitations of prognostic estimates.  ''Every person is different. I can only tell you what usually happens to patients in your situation, not exactly what will   happen to you.'' Check for patient understanding.

E: Emotion/Empathy Acknowledge patient emotions. Use NURSE acronym to remember ways to respond to emotion.  

N: Name   U: Understand   R: Respect   S: Support   E: Explore

Answer questions.

S: Summarize/Strategize Summarize and check for patient understanding. Assess patient goals. Avoid abandonment by establishing a follow‐up plan for patients and caregivers that ensures regular contact.

Breaking Bad News: An Evidence-Based Review of Communication Models for Oncology Nurses

Preferences of cancer patients regarding communication of bad news: a systematic literature review.

  • 1
    What is a CBC? What do you mean by "prof"? Were you in medical school so this "prof" was the patient's doctor?
    – Catija
    Commented Jun 13, 2018 at 21:56

What to do

Firstly, there's a chance that what you've discovered isn't conclusive. Before you attempt to tell him, try to think of some ways of verifying your claim. Consult some experts on the subject if you can.

If you can confirm your suspicions or can't confirm either way, then you should let him know.

How to do it

The same way you tell anyone something very important and potentially life-changing. Sit him down in a quiet room somewhere, preferably at home (his or yours), either alone or with your mother, and then tell him the truth.

He might already know, he might not. Either way it's important to be open and honest and to let him know what you've found.

In my experience, the harder it is to tell someone something, the more important it is to tell them. Keeping secrets and hiding the truth is usually just delaying the inevitable.

Remember that whether your grandfather was your father's biological father or not is nowhere near as important as the fact that your grandfather raised him. I find that people often hold biological relationships above actual personal relationships, but blood isn't always thicker than water. For all intents and purposes, your grandfather is still your father's father in every aspect but biology. Be sure to remind your father of this.


I acknowledge that many people are saying "don't tell him", but I disagree.

Sure, it's going to be upsetting if he doesn't know already, but if you keep it hidden from him then it's going to keep playing on his mind. Chances are you'll eventually cave in and tell him anyway and he'll be wanting to know why you kept it from him for so long, which is going to be far more detrimental to your relationship than if you're honest with him from the start.

It might seem catestrophic, but as I said before, it doesn't change that your father's father was the one who raised him. It doesn't magically undo all the things his father said or did. The father who raised him is more of a father than his biological father is.

The sooner he learns the truth, the sooner he can come to accept it.

@Astralbee's argument that there might be a medical impact of this revelation is also important. For example, certain heart conditions can be inherited.


This goes against my better judgment in that I think you most definitely should not say anything about this, but I'm going to offer advice on how to do it. First of all, ask yourself: what do you hope to have anyone gain by this? Approach this from that vantage point.

You make the assumption that he doesn't already know about it. That needs to be found out. Otherwise you are dragging up something that you he already knew about and kept quiet.

Grandmother's dementia most likely means that you won't get any kind of truthful answer out of her. Depending on the severity of the dementia, she may think you are someone else, she may just not remember, or she may remember something that never happened. I wouldn't approach her. You may not even get consistent responses out of her, depending on her lucidity at the moment.

You only bring up things with the rest of the family present when you are doing an intervention. Think about it: how would you feel if everyone were gathered around when your son told you that your mother slept around? How would you feel? Also, what do you hope to do by bringing the other chap's family into this? I can't see that having a positive note there either, especially if there's no proof. So leave the other family alone. This is long in the past and should stay there.

The only way I can see to do this is to meet with your father privately. Explain to him what happened - you had a DNA test done, and the results were not what you expected. Watch your father's reaction. Keep in mind that this may destroy his feelings about his parents, so you are on very unstable ground here. If it even looks like he may not want to discuss this further, then WALK AWAY and say nothing more. Be prepared for him not wanting to speak to you ever again. Think about this - how would you want to find out that your father wasn't your father? What would your reaction be? Your father's reaction will most likely be similar. Only discuss what are facts - you had the test done, and the results were what they were. Your theories at this point will only toss more gas on the fire.

After this is done, say nothing about this to anyone - ever. This is not your story to tell publicly. I would find this incredibly embarrassing if it were me and would not want my mother's reputation/memory challenged in this fashion, especially if she's not able to defend herself.

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