HappyBanana
Is it such a stretch that the Doctor would consider himself to be Susan's father? Even if it is just an adopted title? ninja
She called him "grandfather", so I don't think the Doctor was referring to Susan when he told Rose he was once a father. Or maybe he was. Quite frankly, I could care less either way.
As of this writing the Outpost Gallifrey thread on the "I was a father once" line, which once again reignited the debate about Susan being or not being the Doctor's biological granddaughter (and the canonicity of Lungbarrow, Cold Fusion, etc. etc. etc.) is now 253 replies deep. Methinks this is an issue which will never be completely decided until the Doctor explicitly and irrefutably says something one way or the other on TV. And even then a few people will still find a way to argue the opposite. gonk
Meanwhile, RTD is probably laughing his head off somewhere...