About a month ago, a friend I haven't heard from in some years invited me for dinner. We decided on a date that worked for both of us but I forgot to add it to my personal calendar. I was not particularly excited for this dinner but since I had no other plans, I accepted the invitation.
A few days ago, I received an invitation from my parents to join them for dinner in a nice restaurant tomorrow. My calendar showed no other plans so I told them that I would love to have dinner with them; they confirmed the reservation in the restaurant.
Today, my friend sent me a text related to his invitation of last month (about some things I should not forget to take with me). Upon receiving the text, I realized I totally forgot about this dinner with him and it so happens that it is also planned for tomorrow.
While my friend was obviously the first to invite me over; I much prefer to have a nice dinner with my parents instead. Still, I realize it would be very rude to simply tell my friend that "I forgot about our dinner and already made other plans so I won't be coming over".
How can I politely communicate to my friend that I want to cancel the planned dinner?