Music mogul Simon Cowell has revealed his biggest business mistake and admitted that it is not signing girl group the Spice Girls when he had the chance to.

Speaking to Jay Leno on 'The Tonight Show', the superstar explained that he regrets not being involved in the amazing collective career of the 'Wannabe' beauties as he was once in the position to be more hands on:

"What can I admit to? Spice Girls was probably my biggest mistake. I knew they were going to big and I offered them a deal but I was just too late on the deal and they didn't want to sign to me, that kind of hurt at the time."

Cowell then added that Westlife originally auditioned for him, too, but once again he didn't work with them: "I quickly put together another group. Well another group auditioned for me. They were called Westlife. When they first came along they were the ugliest boyband in the world. So seriously you couldn't get uglier. I said to the manager at the time, 'Forget it.' Then he re-auditioned but one of the ugly ones dyed his hair blonde for the second time I saw them and he got back into the group."

"I didn't recognise him but it all worked out fine. They sold about 50 million albums or something so it all worked out well enough."