The former X Factor judge and her boss Cowell are said to have slept with each other several times.

The claims made in Cowell’s new biography, have heaped renewed personal pressure on the Aussie songstress, who is licking her wounds over a break up of her relationship with Kris Smith, the father of her first child.

The book, entitled Sweet Revenge: The Intimate Life Of Simon Cowell, written by former BBC journalist Tom Bower, describes a conversation Cowell had with a pal, in which he said: “There were a few bonks and then it petered out while I was in America.”

The book was peppered with other quotes referencing the alleged liaison, even though Minogue and Cowell both denied it in 2008 – before she got with Smith – when it was alleged to have taken place.

Cowell is also quoted in the book saying: “I had a crush on her. It was Dannii’s hair, the sexy clothes and the t**s. I was like a schoolboy. She was foxy. She was a real man’s girl. Very feminine.”

Minogue’s friends are worried about how she will deal with the claim.

A friend told the Mirror newspaper: “She is incredibly raw and this is the last thing she wants to endure.”

The friend added: “Dannii was very much collateral damage in all of this. It’s betrayal, pure and simple.

“And it looks very much now like Simon simply hired Dannii, used her, then spat her out afterwards.”

Cowell is also said to be outraged over the quote in his book. It is claimed he did not know what Bower would write.

However, another friend of Minogue dismissed his ignorance, and said: “Simon is the biggest control freak ever. Everything in his world is controlled to within an inch of its life and it’s very hard to believe that he wouldn’t have known this was set to come out and not have tried to stop it through legal routes if he really wanted to.”

In 2007 Minogue was forced to deny that she was close to the X Factor mogul after a photo emerged that appeared to show the pair holding hands in the back of a car.

She said at the time: “We were not holding hands. But no one believes me. It was the angle of the picture.”