The 25-year-old actress - who played the Doctor's assistant, Amy Pond in the BBC series - took to the stage with her signature red locks.
But all was not quite as it seems, as that red hair was actually a wig, which she whipped off to reveal a grade 1 buzz cut.
Karen shaved her bonce for her latest role in 'Guardians Of The Galaxy'. She plays evil pirate Nebula in the Marvel movie, which is due to hit the big screen next year.
Speaking about shaving her hair off, she said "It's liberating. "I think everyone here should shave their heads."