Cowell signs up Ri-Ri as US X Factor mentor despite her being too raunchy

London, Sept 13 (ANI): Music mogul Simon Cowell has signed up Barbadian singer Rihanna as a 'US X Factor' mentor even though he had earlier found her to be too raunchy.

Rihanna, 23, who is the second star signed as a judge mentor after Mariah Carey, will be L.A. Reid's sidekick when he cuts down his final four acts.

"Simon loves Rihanna and loved having her on the UK show last year - so it's no surprise he wants her back," the Sun quoted a source as saying.

"He hasn't officially announced her yet as he loves keeping everyone guessing. But fans are already getting excited," the source revealed.

The US X Factor will air on ITV2 on September 22 - the day after its premiere in America. (ANI)