I thought [River’s story] was properly over with The Name of the Doctor. I mean, I wasn’t sure, but I thought she had to have a farewell scene with Matt Smith, because they’ve had so many stories together, so I wrote that big ending for the two of them. But I knew we hadn’t done River’s real ending. It didn’t even bother me that we might never see it. There’s a whole load of stuff that the Doctor and River get up to that we never, ever see and never, ever should. There are adventures we’ve never seen, and there are rows in restaurants. They’re probably king and queen of some island somewhere. We’re not going to join all the dots, because it loses all the fun if you do. You’ve got to think, ‘That stuff’s been going on, but that’s their business.’ The Doctor hasn’t deigned to tell his BBC biographers any of that story because I think he’s faintly embarrassed by it.
— Steven Moffat on River and the Doctor (DWM 494)