Simon Cowell

Simon Cowell is leaving American Idol after its ninth season concludes in May, he announced Monday.

Cowell, one of the three original Idol judges, will launch an American version of the British show The X-Factor, which will air on Fox beginning in the fall of 2011, he announced at the Television Critics Association winter tour in Pasadena, Calif.

Simon Cowell will leave American Idol, his brother says

"Where we have come to and what we've agreed is that X-Factor will launch in America in 2011, with me judging the show and executive producing the show," said Cowell. "Because of that, this will be my last season of American Idol this year. Thank you for your patience, but that is what's happening."

To underscore the news, Fox entertainment Chairman Peter Rice had Cowell sign his new agreement with the network onstage before a room filled with reporters.

Simon Cowell to bring X Factor to the U.S.?

"I said this was my last season on American Idol. Everyone thought I was negotiating," Cowell said. "I was offered a lot of money to stay on, but that wasn't the reason behind it."

Rice said that the network plans to air X-Factor in the fall, American Idol in the spring and So You Think You Can Dance over the summer. "I wouldn't have put X-Factor on if I didn't think it could exist separately," Cowell said. Though Idol and X-Factor are both singing competitions, X-Factor has no age limit and conducts live auditions. The judges also mentor the contestants.

Fox announces Idol schedule

Cowell follows original judge Paula Abdul, who departed this summer after eight seasons with the show. Abdul's new replacement, Ellen DeGeneres, recently told Entertainment Weekly she would leave if Cowell departed Idol but changed her tune upon the announcement.

"He announced he's leaving on my first day.  I'm trying not to take it personally. But seriously, I am going to be very, very sad to see him go, because I think he's made the show what it is ... I wish him all the luck in the world hosting The Tonight Show," DeGeneres joked on her show, which airs Tuesday.

"I'm confident that [Idol] will continue to be the No. 1 show and everyone is committed to keeping it that way," Cowell said.

Season 9 of American Idol debuts Jan. 12 at 8/7c on Fox.