The Doctor and Ruth in “Fugitive of the Judoon”

Both of you can only be my past. But that's impossible because I know my own past- I lived through it. All of it.

You're wrong.

I'm not wrong! I've seen Gallifrey destroyed. Twice. First by war, second by a lunatic who I'm still trying to find. In my time, Gallifrey doesn't exist. It's gone! Forever. And if you don't know that, you're in my past. So you are only serving for the glory of ash and bone.