The Beliebers and Directioners may have some serious competition with a rising new fan base. British actor Benedict Cumberbatch has found himself with a fierce group of supporters in the so-called "Cumberbitches," and according to one of his costars, they are not to be messed with.

Keira Knightley, who acts alongside Cumberbatch in The Imitation Game, opened up to Seth Meyers on Late Night about her colleague's loyal fans. 

"You got to work with Benedict Cumberbatch, who you worked together with eight years ago," Meyers, 40, began, referencing 2007's Atonement. "You've really seen the explosion of how ladies have lost their minds."

"The Cumberbitches," Knightley, 29, prompted.

"They've become a thing!" Meyers exclaimed.

The Begin Again star noted that the fans are much more than a "thing" these days.

"It's terrifying," she admitted. "I mean, they're lovely. I feel terrified saying they're terrifying cause they might come after me. So… yes, it's amazing! They're very artistic! They paint pictures of him. You go to premieres and there's these amazing paintings of Ben looking Ben-like… [They're] a very hysterical, artistic type."

Unfortunately for the Cumberbitches, the swoon-worthy star is now off the market. Cumberbatch, 38, announced earlier this month that he is engaged to his theater director and actress love Sophie Hunter. Despite his unavailability, the star's fans haven't wavered.

"I actually had a really embarrassing moment at the London premiere, because — they really do — they scream more than I've ever heard for anyone else, but I had a publicist with me and she went, 'You know, go sign some autographs,'" Knightley explained. "I went over there and went 'Oh yeah, of course, of course, no problem!' And they were like, 'Oh no, we don't want you. We're just here for Ben.'"

Watch Knightley give her two cents on the Cumberbitches in the video above!