Randy Jackson is the hardest judge to impress on American Idol, Nigel Lythgoe has revealed.

Nigel, who is the show's executive producer, described the sole remaining judge from the original line-up as the Simon Cowell of the panel, because he doesn't mince his words.

"Randy, in truth, is the tough one. When other people couch their 'No, you were c***', Randy says it, and 'Give up singing. You're never going to be a singer'," he said.

Mariah Carey, Nicki Minaj and Keith Urban are the new judges on the US singing show, but they're not as blunt as Randy.

Nigel continued: "You can see the other three judges wouldn't because although they may agree with that outright sentiment, they certainly feel like they're not there to hurt anybody. Where possible they will try and send them away with either a good comment of how they can improve or a suggestion of what they move on into."

The TV boss also talked about how country singer Keith - the husband of actress Nicole Kidman - has had to deal with the feud between Mariah and Nicki.

"This is the first time I think that we've had a country judge and he is such a lovely man. He is the scratching post between Mariah and Nicki," he said.

"He sometimes looks like he's watching a tennis match with his head bobbing between the two girls, but when it's his turn to speak he gives his mind and he won't put up with anybody else knocking him down. He's had rounds with Mariah, Randy, and Nicki; a big one with Nicki, in truth. Keith is a great addition this year."

The new season of American Idol can be seen on 5*.