Simon Cowell has outted Irish music mogul, Louis Walsh, as the biggest diva backstage on "X Factor".

Cowell said that Walsh's rider list contract includes toys and a pedigree puppy. He said "Louis is the biggest diva I've ever worked with - he is so demanding it's unbelievable…His rider for when he comes on the show includes things like a puppy, a pedigree puppy. He requires certain drinks, specific foods. He even has to have toys to play with. It's the biggest list of demands I've ever seen."

The pair are joined on the show by celebrity judges Nicole Scherzinger, Katy Perry and Pixie Lott. Cowell said that Walsh made a beeline straight for Scherzinger when she appeared on the show.

"Louis around Nicole was just like a little puppy who's got their first toy to play with and won't leave it alone. He just kept looking at her. Wherever she went he just stared at her…At lunchtime he was running around getting her things to eat and drink. He even made her fish and chips. He was actually cooking for her! If he could have literally could have laid down on her lap he would have."

Cowell added "We had to intervene a couple of times just to tell him to leave her alone. I think Nicole was amused but the two of them did get on very well, very quickly."