Simon Cowell has blasted former 'American Idol' colleague Nigel Lythgoe for being "unprofessional".

The music mogul has branded the executive producer of the talent show "disrespectful" after he said the programme - which is judged by Aerosmith frontman Steven Tyler, record producer Randy Jackson and 'On the Floor' singer Jennifer Lopez - was a "lighter" place since Simon quit as a panellist in 2010.

Simon explained: "I called him out on it. I said, 'Nigel, even if you feel that way, you've got to remember that I put nine years of my life into that show and was part of the reason it became such a hit.

"This is unprofessional, it's disrespectful, and it's not what you should be doing as a human being and as a producer. So just stop it.' And it stopped. It was stupid."

The 51-year-old businessman revealed the reason he left the show was because he did not like the negative attitude.

He added: "All of us, Nigel, myself included, we're Brits who've been allowed to make shows In America which are hopefully going to do well. So enjoy it. Why do you want to be negative? That's why I left the show, because I just didn't like that attitude."