I'm interested in the conception of the River Song story. In 'Silence in the Library,' did you already know she was going to be the daughter of a companion?
Oh no, no. I mean, it was one possible theory. Why is it somebody who's got such connections, who would that be? Is it just a future companion? What if it's somebody's got a lifelong commitment to the Doctor or his companion? So when I introduced Amy, I kept my options open [and used the name Pond]. I thought I was doing [the name thing] in plain sight and nobody [caught] it for a long while. But I didn't know at the time Karen was going to stay long enough for that story to come off. I didn't know if Alex would keep coming back.
Thanks to Combom & Planet Gallifrey