Simon Cowell just admitted what we all knew just by watching the show: Britney Spears was very "uncomfortable" being a judge on "X Factor."

In an interview airing Tuesday with Ellen DeGeneres, the father-to-be reveals why he chose the pop star in the first place ... and why she won't be coming back.

"There was a time I think everyone was trying to up them selves, in terms of who could find the biggest known stars to be on a panel," Simon admits.

"We said 'We’ll take Britney,'" he continues. "She was fine but I think she found it very uncomfortable."

Check out the video above to see what Simon specifically says she didn't like about being on the show.

The new season of "The X Factor" kicks off Wednesday night on FOX, with Kelly Rowland, Paulina Rubio and Demi Lovato joining Simon on the judging panel.

Will you miss Britney ... or are you glad to see some new blood on the show?

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