"All the time," Knightley confirmed when 40-year-old Corden asked her about mistaken identifications. "I've been chased through an airport as Natalie Portman. I mean, Natalie Portman [happens] a lot. I did the Star Wars thing, so I have had many pictures with Natalie Portman."
She continued, "I've been chased through a park by Kate Winslet. Quite a few people have come over to me to ask me to say hello to Daniel Craig for them because they think I'm [his wife] Rachel Weisz. She's lovely!"
But perhaps the most surprising case came when a Los Angeles, California, when a fan thought the Begin Again star was Britney Spears.
"Shut up!" Corden exclaimed following the reveal.
"The other ones I get; English, actresses," Knightley said. "... I don't know, it was a weird one. I had my picture [taken] as Britney Spears."
"I would love to see that person with their friends," Corden responded. "I'd love to see them going, 'Guys, I just met Britney Spears. Look!' And they go, 'My God! ... No, you didn't. You met Keira Knightley.'"
Knightley takes all the misidentification well, even revealing that she minds her manners more when fans think she's someone else."I quite enjoy it, though," she said. "I'm much more polite, I think, when people think I'm somebody else."
"See, I'm not," Corden contradicted. "If people would ever think, not that they ever would, that I was anybody else, I would be awful. If someone came up and went, 'Wow Matt Damon's put on a few pounds. Will you sign this?' I'd just be like, 'Leave me alone you a**hole. Just leave me alone!'"
Also on the late-night show on Tuesday was actress Kathryn Hahn, who dished about a celeb doppelganger of her own. "[I'm mistaken for] Ana Gasteyer," the 45-year-old Hahn said. "All the time. From SNL. So often."
Following the reveal, Corden held up a photo of Hahn and Gasteyer together, which confirmed their similar appearances.
"Look at that, you guys! That is kind of bananas," Hahn said. "She actually told me that when Bad Moms came out, she would go to Starbucks and she would order something and then they'd give her the cup that'd just say 'Carla,' which was my character's name from Bad Moms. They would just preemptively [do it]."
She continued, "People come up to me all the time and say, 'Love you on SNL' and I say, 'Thank you.'"
Knightley's latest film, Colette, hit theaters earlier this month. Prior to its release, ET caught up with the actress and her co-star, Dominic West, where they opened up about the flick. Watch the video below to see what they had to say: