The 29-year-old actress is used to fans mistaking her for Natalie Portman, but says her other supposed doppelgängers are more surprising.
"Natalie Portman I get a lot, and I get chased through airports," she reveals on The Graham Norton Show. "I feel quite sorry for her because she must get chased a lot because it's happened like five times where someone's been like 'NATALIE, NATALIE, NATALIE.' And I'll sign and take a picture as Natalie."
"I get Kate Winslet as well," she continues, "but the one that's surprising is Britney Spears."
"I get quite excited because I like the idea that I could do like that [mimes shimmying], which I can't do," she elaborates. "So I've been Britney Spears like three times. ... [I] definitely sign, and have a picture. Absolutely."
Knightley's first Hollywood film role was Sabé in Star Wars: Episode I - The Phantom Menace -- a handmaiden and lookalike decoy for Natalie Portman's Queen Amidala. The actress has gone on to star in over a dozen big-budget films, and will next appear alongside Benedict Cumberbatch in The Imitation Game on November 21.