(CNN) -- Longtime "American Idol" judge Simon Cowell said he'll be leaving the popular Fox talent show at the end of the season, the network announced Monday at the Television Critics Association press tour in Pasadena, California.
Cowell's popular U.K. talent show, "The X Factor," will be coming to the United States in the fall of 2011 with the acerbic critic in tow, according to Fox.
"I want to leave 'Idol' this year bigger and better than it was in the past," Cowell said at the TCA tour Monday.
Cowell will be both executive producer and judge on "The X Factor."
"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," said Cowell in a statement. "We have a fantastic relationship, a great team and are all very excited about this." iReport: Will you watch "Idol" without Simon?
Speculation has raged for weeks as to Cowell's future. Though he's well paid for his "Idol" work -- an estimated $36 million per season -- he has expressed a desire to focus on "The X Factor."
Cowell said at the press session that it's taken some time to reach an agreement for his new duties, hence the buzz. (Indeed, he signed the last page of his "contract" on stage with Fox executives Peter Rice and Kevin Reilly.)
"[I] didn't think it was right to do two shows in America at the same time, so [I] decided to leave one and start another," he said.
He said he missed Paula Abdul, the former "Idol" judge who left the show in August, but wouldn't confirm or deny whether she would appear on "X Factor" in the U.S. Cowell and Abdul had a good-naturedly contentious relationship on "Idol," with the tough-minded Brit often acting as bad cop to the "Forever Your Girl" singer's good cop.
Ellen DeGeneres, who's taking over Abdul's judging slot, joked about Cowell's announcement on her talk show Monday -- getting in a dig at NBC's late-night troubles as well.
"So this just happened, Simon Cowell just announced that he's leaving 'Idol.' This will be his last season. He announced he's leaving on my first day. I'm trying not to take it personally," she said. "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. He's a huge part of that show but he wanted a change. I wish him all the luck in the world hosting 'The Tonight Show,' " said DeGeneres, referring to widespread speculation about how NBC will resolve its issues with its late-night talk shows. In reality, of course, Simon Cowell has not been part of that speculation.
Since its premiere in 2002, "Idol" has been an entertainment phenomenon, regularly ranking as TV's top show, creating several musical stars and pulling in millions more viewers than its closest competition. Its new season premieres Tuesday.
Cowell's presence has been credited as a major reason. The British music executive was a judge on the British version of "Idol," "Pop Idol," and came to the United States when Fox imported the show. Unlike judges on many American talent shows, Cowell didn't sugar-coat his criticisms to contestants.
With the show's growing popularity -- by its fourth season it was the top show on television, a rank it has held ever since -- Cowell and fellow "Idol" players Abdul, judge Randy Jackson and amiable host Ryan Seacrest became stars in their own right.
Though the show continues to dominate American TV, ratings have started sliding in "Idol's" past two seasons. But Cowell told the TCA audience he had no doubt about the show's future.
It will "continue to be the No. 1 show" in the country, Cowell said. The show has given him "the best days of my life."
Asked who should replace him, he jokingly suggested Seacrest, with whom Cowell has also good-naturedly tangled. The Fox executives said they're not going to rush to find Cowell's replacement.
CNN's KJ Matthews contributed to this story.