Simon Cowell is more proud of Leona Lewis than anyone else from his TV shows.
The 'Bleeding Love' hitmaker has found worldwide fame since winning UK program 'The X Factor' in 2006 and the music mogul is delighted by the way the singer transformed her personality as the competition progressed.
Rihanna turned down a place on the judging panel of 'The X Factor'.
The 'S&M' singer would have loved to accept the offer of a role on the US version of the show by head panelist Simon Cowell, but cannot appear when it launches later this year because of her hectic touring schedule.
Simon Cowell's mother has urged him to cut back on his heavy workload for the sake of his health.
The music mogul is currently juggling the launch of his pop star search show 'The X Factor' in the US with his other presenting and production commitments including UK 'X Factor', 'America's Got Talent' and 'Britain's Got Talent' and his mother Julie is worried about the toll his many responsibilities are taking on him.
Julianne Hough has auditioned for a role on the US 'X Factor'.
The former 'Dancing With The Stars' professional dancer and country music star - who is dating 'American Idol' host Ryan Seacrest - held meetings with Fox executives earlier this week although she could face competition from singer-songwriter Jesse McCartney, who has also met with show bosses.
Demi Lovato is set to mark her comeback with a performance on the US version of 'The X Factor'.
The 18-year-old star - who left rehab in January after seeking treatment for "emotional and physical issues" in November - is in talks with producers of the highly-anticipated TV talent show to perform on one of the live shows after a judging role was ruled out.