It was revealed that River Song is the daughter of companions Amy and Rory (Arthur Darvill). Is this the solution you had in mind when you first introduced her in “Silence in the Library” back in Season 5?
Not quite…It came about from the most practical reason: I had to have the Doctor in a library…and a bunch of archaeologists had to find him and not immediately arrest him for the crime. The psychic paper wouldn’t cover it, so I thought, What if one of the archaeologists knows him?…But then I thought, What if one of the archaeologists knows him, but he doesn’t know the archaeologist? Suddenly, that’s quite cool. What if it’s a woman? What if it’s a woman who flirts with him in a rather proprietary way? Then a whole story explodes in your head…She might be his wife, or a girlfriend, or there’s a romantic attachment there.
When I introduced Amy Pond, it was with the possibility that this could be the mother of River, and that’s why I put the “Pond” in…There was no guarantee that Karen [Gillan] was going to stay or that Alex [Kingston] would come back. It was just a possibility that I kept alive.