"X Factor" judges Simon Cowell and Demi Lovato made a guesting on the Conan O'Brien show last Monday night and seemed perfectly comfortable calling each other names.

Simon Cowell previously guested on the Jimmy Kimmel show together with another "X Factor" judge, Britney Spears. During their interview, the pop singer revealed how Simon lured her into becoming a judge on the "X Factor" and admitted that ruthless judge can be a "sweetheart." Last Monday, it was Demi's time to talk about the British judge.

Simon once called the 19-year-old former Disney star a "brat" but Demi wasn't coy enough to call Simon an "a**hole" on live television. It all started when Conan asked Demi's opinion on Simon's signature white V-neck shirts. There, the young singer found an opportunity to lightly joke about Cowell's "man cleavage."

"We're trying to reach a younger demographic, and I don't feel we're going to accomplish that when he's showing more cleavage than Britney [Spears] and I are," Demi said. "I'm surprised, because normally you could braid your chest hair."

Simon then asked for Conan's help so that Demi would stop picking on him. The host then asked Simon why he refers to Demi as "annoying."

"You are very annoying. How's that?" Simon turned to Demi.

The singer then called him a bit of an "a**hole" on national TV. Simon who has the reputation for being Mr. Nasty has turned himself into Mr. Naughty on his recent late night interviews.

Last month the four "X Factor" judges participated in a press conference where Simon hinted about what the audience should expect from Britney and Demi.

"Demi is a brat. But there's something likeable about her. Britney's quite mean, as you'll discover," he said.

Also read:

Britney Spears Shares How Simon Cowell Lured Her to Judge 'The X Factor': 'I fell in love with him'

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