Signing his formal agreement on stage as a surprise guest at the Television Critics Assn. gathering in Pasadena, Simon Cowell left no doubt: This … is his last season on "American Idol."

In 2011, Cowell will appear on camera as judge and exec produce the long-anticipated premiere of "The X Factor" on Fox in Fall 2011.

"There's been a lot of speculation (about my future) partly because we didn't have an agreement," Cowell said. "We've reached an agreement formally at about half past (11) this morning. That's the absolute truth. We've agreed 'X Factor' will launch in America in 2011 with me judging the show and executive producing the show, and because of that, this will be my last season on 'American Idol' this year.

"We did talk about me staying on both shows, but when we looked at the practicalities of that, it was just impossible."

"We're incredibly committed to 'American Idol,'" Fox entertainment chairman Peter Rice said, "Simon is irreplaceable, but it's going to be incumbent upon us to make sure the show remains vital and entertaining. People are in love with the format, and we have to come up with a (way) to keep that energy going."

Among other things, the launch of "X Factor" will allow Fox to keep "So You Think You Can Dance" in the summer, where it has performed better than it did this past fall.

One of the strengths of "X Factor," says Cowell, is that there is no age limit for contestants.

"One of the best examples of that is ('Britain's Got Talent' success story) Susan Boyle," Cowell said. "Without a show like that, she could not have landed a recording contract. … One of the goals of 'X Factor' is to find the American version of Susan."

Like "Idol," "X Factor" will have separate performance and results shows each week, Cowell said.

In a response that directly echoed his comments at last summer's TCA, which came just as Paula Abdul was announcing her departure from "Idol," Rice asked for patience as they searched for a judge to replace Cowell, citing the importance of "chemistry" between the judges. (He also declined to take the bait offered by a reporter who asked if this was a good time to dump judge Randy Jackson.)

"We love the interaction between (the judges). We specifically love Randy," Rice said. "We're not going to try to find a Simon clone that can do what he does, because he's one of a kind."

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