When Keira Knightley played Britney Spears' double

Actor Keira Knightley says she is often mistaken for other celebrities, but she couldn’t resist playing along when a fan thought she was popstar Britney Spears.

Actor

says she is often mistaken for other celebrities, but she couldn’t resist playing along when a fan thought she was popstar

.

On a TV chat show, Keira said, "It has happened to me three times in LA. I was quite excited by that and definitely signed and had a picture."

But Knightley admits she has very little in common with Spears because she hates singing in public, reports contactmusic.com.

"I like singing if I’m on my own in the shower or if I am really drunk, but I’m not a big fan of singing in front of people," the 29-year-old actor said.