London, Dec 14 : Simon Cowell had to apologise to Beyonce Knowles for branding her `not sexy' before she could agree to be the special guest on `X Factor' finale.

In an astonishing public tirade against the singer, Cowell described her as "not sexy".

He said: "I find the whole Beyoncé thing really mystifying. She's not sexy, she hasn't got a great body and she's not a great singer."

The extraordinary statement in Esquire magazine three years ago prompted the singer's tough producer father, Matthew Knowles, to say: "Simon wouldn't know a hit song, image or talent if it hit him in the face."

Meanwhile, producers of X Factor pointed out that only a really big star could help trump the ratings of the show and the only performer with that kind of pulling power was Beyoncé.

Therefore, as long as two months ago, Cowell began his campaign to make amends with Beyoncé.

"It's debatable whether she'd have agreed to the X Factor at all if she didn't have a CD to promote," the Daily Express quoted a source, as saying.

"There's been bad blood between her entire family and Cowell ever since his ridiculous rant in Esquire. Believe me, it took a lot of apologising on his part to swing it. At the end of the day, she realised she has a big fan base in Britain. She's appearing for them, not for Simon Cowell," the source added. (ANI)