Britney Spears and Demi Lobato joining the judge panel in "The X Factor"

Fox has formally announced that pop singers Britney Spears and Demi Lovato are joining "The X Factor." They will join Simon Cowell and fellow returning judge L.A. Reid during the Upfront Presentation in New York City on Monday afternoon.

Prior to the reveal, Britney posted a photo to her Twitter page, with the hashtags #britneyxfactor #SimonBritneyDemiLA, showing the pop princess with her new co-workers: Simon, LA Reid and Demi. See the photo, HERE!

Britney and Demi (whose first official "X Factor" promo photos appear above) will replace the departed Nicole Scherzinger and Paula Abdul, who left the show after one season, along with host Steve Jones.

"Not to be negative about the people leaving, but we just felt the mix could be more effective and more entertaining," Peter Rice, entertainment chairman for the Fox Networks Group, told reporters earlier in the day on Monday.

Back in February, Simon spoke to Access Hollywood's Billy Bush where the reality mogul said "X Factor" would be a "walk in the park" for Britney.

"I'm fascinated by [Britney.] The fact that she's one of the most talked about - not just pop stars - but people in the world today, means that you've got this star power," Simon told Billy at the time. "This girl has got resilience. I would think that if she's managed to sustain a family, a career, which is tough, ['X Factor' would be] a walk in the park."

While Simon is clearly impressed with the chops Britney will bring to the table, not everyone appears to agree. During a press conference earlier this month, new "America's Got Talent" judge Howard Stern said he doesn't think the pop princess will bring much to the judges' table.

"As far as any real criticism, I think Simon [Cowell] and L.A. Reid will be doing that. I think Britney is going to stand there and eat a lollipop and wear a sexy outfit. I don't anticipate great opinions out of her," Stern said. "I think she's going to sit there like J.Lo and [say], 'Oh, you're wonderful. You're terrific. Do you think I could get a perfume endorsement out of this? You think I could perform on the show?' I think that's what it's about.