The Atonement beauty is known for her tall and slender frame, but her looks once prompted speculation she was battling an eating disorder - and although Knightley was sure she didn't have food issues, she soon started to wonder what was wrong with her body as the rumours refused to go away.
She tells Allure magazine, "I knew I wasn't anorexic. But maybe my body is somehow not right. Or my face is not right. Or the way I speak is not right.
"When you're going through a period where you're really getting a lot of criticism, you go, 'Maybe all this is right!' You just kind of want to hide it all."
However, the British star has since learned to embrace her slim figure both onscreen and off and she insists she has no problems stripping off for the right movie role - but it will only be her breasts on show.
She says, "I'm quite rigorous about what gets exposed. No bottom half! I don't mind exposing my t**s because they're so small - people really aren't that interested!"