Britney Spears has signed a one-year, $15-million contract to join the judging panel on Simon Cowell's The X Factor , E! News reported on Wednesday citing an unnamed source close to the star. "The contract is signed," the source told the entertainment cable/online entertainment outlet. "There's been a lot of back and forth over the past few weeks as they negotiated the small details, but she's on. It's all completed and Britney is beyond excited. ... This is the perfect next stage in her career. Both Britney and Simon are very excited to work together." Spears joins a panel that now includes Cowell and record producer L.A. Reid. E! said that a fourth judge is likely to be announced when Fox unveils its fall schedule on Monday.