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Speaking to the Daily Mirror following Simon's revelations about his relationship with Dannii in 2008, Sharon hit out: "Dannii wanted to be the mistress of Simon Cowell – and the mistress of X Factor."
But the flame haired star, who left the show the year after Dannii joined, insisted: "I didn’t leave the show because Simon and Dannii were f******, I left because she became unbearable. She started bossing everyone around, even the producers.”
The claims appear in a new, supposedly unauthorised, biography of Simon Cowell, written by journalist Tom Bower.
Sharon went on: “We all knew Simon and Dannii were seeing each other, it wasn’t a secret. I don’t know why he tried to hide it from everyone though – he’d already split from Terri.
“But it’ll be interesting whether the book mentions he was seeing Mezhgan, Jasmine and Julia at the same time.”
She added: “All Dannii wanted to do was f*** Simon Cowell. That’s why she was on the show.”
The book, out next month, also claimed that Sharon was "out of control" and Simon wanted to have an affair with Cheryl Cole while she was on the show.