Simon Cowell has revealed that he twisted the truth over reports that Britney Spears had walked out of her first X Factor USA filming.

Spears signed up to appear as a judge on the show earlier this year at the same time as fellow newbie Demi Lovato.

Reports emerged that the 'Circus' star walked off the set on her first day - but it was claimed that she was merely just taking a break.

Speaking to TMZ, however, Cowell has revealed that his team "half-lied" over the incident and that she walked off after a panic-stricken "moment" of self-doubt. He said:

"No one is going to admit that on the first day your highest paid star after 20 minutes has walked off set."

The X Factor supremo added that Spears "had a moment on the first day where she said to me 'I'm not sure I can do this'."

As previously reported, the 'Toxic' star recently revealed in an interview with Elle that she suffered numerous panic attacks on her first day as an X Factor USA judge.