David Tennant, the tenth Doctor Who, is to marry Georgia Moffett, the daughter of the fifth Doctor Who, Peter Davison.
OK, here's the problem. According to the old Fifth Doctor serial Mawdryn Undead, meeting and touching a past or future version of yourself would "short out the time differential" and cause a big explosion. So you can only imagine the results of marrying the daughter of your previous incarnation, and having yourself as your father-in-law. It'll make those family holiday gatherings a bit awkward, to say the least. ("Would you pass the mashed potatoes, please, David?" "Sure, Peter, just let me get these huge lead gloves on.")
Perhaps the Blinovitch Limitation Effect can help?
Then again, maybe it is just a TV show. All the best in the future to the happy couple.