I can’t improve on The Register‘s take:
Doctor Who the 10th, David Tennant, is planning to get hitched to his fictional daughter Georgia Moffett, who also happens to be the real daughter of his fictional fifth incarnation.
Moffet is the real-life fruit of former Time Lord Peter Davison’s loins, and played Who offspring Jenny in 2008’s The Doctor’s Daughter. Davison and his future son-in-law Tennant appeared together in 2007’s Children in Need Doctor Who special Time Crash, well after Ms Moffet really existed, but before she was spawned as her soon-to-be husband’s television child.
Paradoxically, this means that Davison and Tennant came together as both individuals and the same person, while one was the father of the future daughter of the other.
