Rose: When you say nine hundred years…
The Doctor: That's my age.
Rose: You're nine hundred years old?
The Doctor: Yep.
Rose: My mum was right. That is one hell of an age gap. (jumps down off the wall) Every conversation with you just goes mental. And there's no-one else I can talk to. I've seen all that stuff up there, the size of it, and I can't say a word. Aliens and spaceships and things… and I'm the only person on planet Earth that knows they exist.
(At that moment, a large spaceship flies overhead, crashing into Big Ben and landing in the Thames)