Britney Spears has hit back at actress Keira Knightley for slamming her infamous flashing underwear incident.

The Pirates of the Caribbean star branded Spears a "slut" after she was photographed flashing her underwear earlier this year.

But the singer laughed off the comments, adding, "Who's Keira Knightley? I guess she must need the publicity."

- Britney Spears Gallery
- Keira Knightley Pictures

(This news article provided by World Entertainment News Network)