Jenna-Louise Coleman is the new companion, starting at Christmas.
Never seen her in anything (except apparently she was Connie in Captain America - one of the dates at the World's Fair) have to watch ITV's Titanic now.
(I'd never seen David Tennant in anything before he was announced, they reshowed Casanova so those without cable could get a look at him.)
Let the wild mass guessing about who she is begin!
(First mad idea since she's dark-haired and mid-twenties, she's obviously the Doctor's opposite sex clone. For reals.)