I'm a software developer and recently the product owner on my team has been intermittently absent. Her direct boss "Joe" has started attending some of our meetings that she can't make it to. We do agile and try to keep our meetings (scrum, retrospectives, etc...) as close to their intended purpose as possible, and the team has a scrum master (not me) who is present in these meetings. I don't know how much Joe has been exposed to agile, so I'm not sure if he's fully aware of the rigidity with which we try to run meetings.
There have been several instances since Joe started attending our meetings where he will take over the meeting to talk about something other than the intended purpose of the meetings. The things he talks about are still work-related, but they hinder us from being able to complete the goals of our meetings. For example: every two weeks we have a sprint planning meeting for 30 minutes to assign out work for the next two weeks. At our last one, Joe spent 10-15 minutes of the meeting informing the team that we will be getting interns 3 months from now.
I've only just met Joe recently, but others on my team told me they've had this problem with him in the past. I believe that they've tried talking to him about it, but the issue still persists. I talked to my manager about him, and was told that there have been discussions in the past about the issue, specifically the team had a retrospective once where much of the conversation revolved around meetings getting off topic. I don't know if Joe was in that meeting or if he was specifically called out or the team just discussed the general topic of off-topic meetings. I haven't seen anyone do anything in meetings like interrupting Joe to steer the meeting back.
Since I only recently met Joe, I don't know him well enough to have a good idea how he will respond to feedback. One thing I should mention is that I am remote from the rest of my team, so every meeting is them all in a conference room and me calling in via skype.
How can I politely stop Joe when he gets off topic so that he doesn't derail the whole meeting?