That's what he'd thought, too. He hadn't been able to believe it, or hadn't wanted to, when he'd seen the Doctor disappearing in the TARDIS, leaving him behind. He'd tried to tell himself it wasn't what it seemed, that the Doctor hadn't known he'd come back to life, but he can't believe it was an accident.

How could Jack have come back to life but for an intervention by the Doctor? Nothing else makes sense. And then the Doctor left him, alone on a space station full of the remains of Dalek and human defender alike, and he's been looking for him ever since.

And here's this girl, so young, so convinced she knows the Doctor. Like he was once. So full of faith in him.

"Maybe one day I'll get a chance to prove that."

He hasn't seen him in more than a very long century.