"I'm asking because I've got the greatest trait in the world: simple curiosity." Oh, there's more to that than idle curiosity. There's a sense of deja vu whenever he looks at himself in the mirror. But the Doctor's so old and his memory's so spotty that he honestly can't place where he's seen this face before.

So, asking around it is. And honestly? He's going to sound crazy no matter if he answers the question truthfully or continues to dodge it, especially since this girl seems only human. Though there's an oddness about her that he can't place but absolutely loves.

"And because again, I don't know where I've seen this face. I've told you that already." He might not have.