Britney Spears joins judges on US X Factor Spears found fame as a 16 year-old in 1998 with her debut single "Baby One More Time" and went on to score multiple hits with songs like "Crazy," "Oops I Did It Again" and "Womanizer." She had a much-publicised personal and career meltdown in 2007 but made a comeback with her 2008 album "Circus" and a world tour. Lovato found fame on Disney Channel's TV series "Sonny With a Chance" before launching a career as a pop singer with hit singles like "Skyscraper." "Britney remains one of the biggest stars in the world, she's talented, fascinating - and I believe she knows exactly how to spot The X Factor," Cowell said in a statement. Demi's had an amazing career in music, TV and film for someone her age. She's young, confident, and enthusiastic. I think it's really important that she speaks to our younger audience. Spears said in New York, "I'm so excited by this whole experience. It's so different from anything I've ever done. Fox gave no details of their contracts but Spears has been widely reported to be getting $15 million a year for the X Factor gig, which would make her one of the highest-paid TV reality show judges. Mariah Carey, Janet Jackson, Miley Cyrus and Avril Lavigne were among other names rumored to have been approached or in talks with Cowell about taking part in X Factor. Cowell launched the U.S. version of X Factor last September with great fanfare and boasts that it would topple ageing "American Idol" as America's most-watched TV show. But the show mustered only about 13 million viewers - about half the audience for American Idol - and many critics disliked its brash, noisy production and felt it added little new to the crowded TV singing contest field.