The Doctor chuckles softly. "We might be from different universes. Doesn't mean that your Earth has never been invaded. I've spent a majority of my lives protecting that little planet. It would be difficult to convince me of a place where Earth hasn't been a least visited."

Doesn't matter. Other than no one ever knows the amount of work he does. That's good, it makes his work easier when no one knows...

"One or two. This is nearly the oldest I've ever appeared."