The music mogul branded rumours about his sexuality as "mad", and said there was no need for him to cover up anything about his life style.
"If I was gay, why wouldn't I admit it?" Simon told The Sun today. "It wouldn't harm me and my mother wouldn't freak out."
Former BBC journalist Tom Bower makes the same claim in his new book about the reality telly judge, which is set to hit shelves next week.
He said: "The pertinent fact is that not a single man has offered any evidence of an advance by Cowell despite the promise of enormous financial reward."
Other revelations in the book - which have included Simon's apparent affair with Dannii Minogue - have been the source of tabloid front pages for the past week.
The unauthorised biography, Sweet Revenge: The Intimate Life Of Simon Cowell, goes into intimate detail bout Simon's life both on and off camera.