Simon Cowell has opened up about the reasons behind Britney Spears' departure from The X Factor, revealing the singer found her job as a judge "very uncomfortable". Spears joined the panel of the American version of the hit TV talent show, but quit after just one season on screen. Cowell has now revealed he made a mistake hiring the singer, because she hated interacting with contestants and voicing her opinion on the acts. In a taped interview with U.S. talk show host Ellen DeGeneres, he says, ''I didn't realise that (she was not good at talking)! I kind of booked someone who couldn't talk, which is a bit of a problem when you want someone to judge... She wasn't comfortable being negative, she didn't like it when the contestants spoke back to her, so she was just uncomfortable. I liked her. So we decided to change it this year.'' Cowell also admits he became obsessed with chasing star names for the judging panel in a bid to keep up with the show's rivals, American Idol and The Voice. He adds, "There was a time I think everyone was trying to up themselves in terms of who could find the biggest known star to be on a panel. And in terms of a pop singer? Jennifer Lopez and the other one on The Voice... I can't remember. Blondie. Christina (Aguilera). And we said, 'We'll take Britney'. She was fine, but I think she found it very uncomfortable.'' The interview will air in the U.S. on Tuesday (10Sep13).