David Tennant on Doctor Who: "It's a bit like being the President. You're always the Doctor"

And clearly US chat show host David Letterman is one of them.

"Now for God's sakes, what do people know you from?" Letterman asked Tennant when he appeared on his Late Show. "Do they always say, 'Oh you're the guy from Gracepoint or from, er, Church Town or from Doctor Who.' Which of these things do they know you?"

"It was always Doctor Who. It's still mostly Doctor Who," replied Tennant.

"But you're not still Doctor Who?" asks a confused Letterman, before Tennant took it upon himself to explain the sci-fi hit...

Tennant: "It's a bit like being the President. You're always the Doctor."

Letterman: "Who is Doctor Who now?"

Tennant: "Peter Capaldi."

Letterman: "How many different Doctor Whos have there been?"

Tennant: "He's the 12th. But there's also... there's another one so you could say there's been 13. And then there was a movie version so you could say there was 14. Approximately 12."

That covered, it seems Letterman was confident he'd grasped Who's complicated casting history. "So when you're out and about people say, 'Oh, it's the Doctor Who number 11'?" he asked.

But he hadn't. Not quite.

"Erm. I'm 10," replied Tennant.

So close...

http://www.youtube.com/watch?v=o0iOswyqCTk