After months of rumors and speculation, it was confirmed Monday (January 11) that Simon Cowell will leave the judges' panel of "American Idol," America's most popular TV show, to launch the American version of his other talent show, "The X Factor."

In a press release, Fox announced that "The X Factor" will launch in the U.S. in fall 2011 with Cowell, creator of the show he launched in the U.K. in 2004, serving as both executive producer and a judge on the U.S. version.

Cowell announced his "Idol" departure at the Television Critics Association Press Tour, according to Entertainment Weekly. "We did talk about me staying on both shows but when we looked at the practicalities of that, it was impossible," Cowell told the press. "In my opinion, it's like having a good player and a good football team. The two have to be OK together. I believe it's not my show, but it's still very close to me. We made sure when we did this, that I would be protected. I'm confident it will continue to be the #1 show. Everyone is committed to keeping it that way."

Cowell followed the announcement a short time later by tweeting "I have had the best 8 or 9 years of my life doing this show."

"The X Factor," which is currently shown in 17 countries worldwide, is a singing competition in which contestants square off against each other with the help of professional mentors. Cowell has been eager to bring the show to the U.S., and he will continue to both executive produce and judge the U.K. version after the American one launches.

"I'm thrilled that we have put a date on the launch of the U.S. version of 'The X Factor' and delighted to be continuing to work with FOX," Cowell said in a statement. "We have a fantastic relationship, a great team and are all very excited about this."

Fox has not announced who might replace Cowell on the judges' panel when he leaves the show, and a spokesperson could not be reached for comment at press time. The acerbic British music executive — who has helped launch the careers of Leona Lewis and Susan Boyle, among others — is considered the most influential voice on the "Idol" panel, and his quip-filled put-downs and comments have provided countless water-cooler moments over the show's eight seasons.

The ninth season of "Idol" kicks off Tuesday at 8 p.m., and in their first joint interview, Cowell and new judge Ellen DeGeneres joked about his possible departure, with DeGeneres, who signed a five-year contract with the show, saying, "If Simon goes, I go! I will not be there without Simon." It was unclear from the interview if DeGeneres was being playful or serious about her feelings about Cowell's potential exit.

Get your "Idol" fix on MTV News' "American Idol" page, where you'll find all the latest news, interviews and opinions.