Britney Spears, Simon Cowell, Demi Lovato and L.A. Reid Britney Spears, Simon Cowell, Demi Lovato and L.A. Reid

It's all about prickly, teasing chemistry and banter among Simon Cowell and new The X Factor judges Britney Spears and Demi Lovato.

"Demi is a brat,  but there's something really likable about her as well" Cowell says at the Television Critics Association fall previews for Fox on Monday. "and Britney's quite mean, which you'll discover."

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When Lovato chimes in to defend Spears as a "sweetheart," Cowell snaps, "as sweet as a lemon."

The pop princesses have come on for the reality competition show's second season (premiering Sept. 12, 8/7c, Fox), replacing Season 1 judges Paula Abdul and Nicole Scherzinger. "Because [X Factor] has such a young audience, we needed someone a bit younger [as judges]," he says. "It's worked brilliantly."

Check out nine more highlights from The X Factor panel from TCA:

1. No, really, Britney's a good judge. "They're harder to please than me or L.A.[Reid] ... and very happy to give people a 'no,'" says Cowell. "The fact that Britney's been a pop princess for so many years is a testament to her star power. So unfortunately, I have to agree with her some of the time."

2. Mariah isn't mean enough. "I'm happy for her, actually," Cowell says about friend Mariah Carey being announced as a new Season 12 American Idol judge. "I like Mariah, but I think she's going to find it difficult to say 'no.' She's sweet, but I think she'll be great."

3. The host(s) to come. The show is looking at a wide range of applicants, including those who haven't hosted before, and very likely will go with one male and one female host. "We're screen-testing in the next three to four weeks," says Cowell. "We'll make an announcement around mid-August."

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4. The Britney-Simon pancake connection. "I was such a fan of the show, and my makeup artist was the makeup artist for Simon," Spears reveals. "It made sense [to join the show], and it was something I really wanted to do... I've been able to help this talent that comes in and achieve their dreams."

5. No Rachel Crow redux. Cowell isn't too worried about a repeat of teenager Rachel Crow's public meltdown when she was eliminated from Season 1's Top 5 after a judges' voting deadlock. "It was difficult, wasn't it?" he says. "That was [Paula and Nicole's] fault, wasn't it though? Because they could have saved her. I don't think it would happen again... Rachel has done a lot of incredible things since leaving the show, so there are no scars."

6. Speaking of disturbed youth... "My little sister is in the industry. I worry about her all the time, but she's doing great," says Lovato, who once pulled out of a tour in order to get treatment for bulimia and self-injury. "I think that you can't prevent anyone from going down the wrong road. If they're going to have an eating disorder, they're going to have an eating disorder. I don't really think fame has a lot to do with it. It adds some pressure and sometimes it makes the problem a little bit worse, but for me, I had been struggling with those issues beforehand. Unless you're in a good place when you start working, I think it's kind of inevitable for those things to happen."

7. Don't expect MC Britney. "I'm a huge fan of hip-hop. I love rap," Spears reveals. "But I don't rap."

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8. Respect Demi's authority! "The expertise I'm able to contribute is I'm listening to the radio right now, and I know what my friends like — they're in the early 20s and late teens. And there's a much younger demographic in the competition. We know what is needed in this industry, what's missing."

9. A second "Skyscraper" cover? After Reid demonstrated ignorance of Lovato's song "Skyscraper" last season ("You're doing songs for people who are 40," he told contestant Drew Ryniewicz), the judge ate crow when the teenager joined the judges' table. "I definitely haven't let him live that down," says Lovato. "I can sing it a little if it will help, from top to bottom," Reid says. "I plan to audition for X Factor with that song."

The X Factor will air Wednesdays and Thursdays this fall at 8/7c on Fox, beginning Sept. 12.