Life inside Prince Charles' inner sanctum is to be revealed in an "explosive" unauthorised biography by Tom Bower.

The biographer who revealed Simon Cowell's affair with Dannii Minogue claims the book will include the testimony of more than 120 people employed by Clarence House who were "welcomed into the inner sanctum".

The biography about the 69-year-old heir to the throne is said to be "warts and all" and will be released in March.

Bower said: "There are a lot of revelations. I was amazed how much new material there was. It's got a lot of very, very new, untold information," The Mirror reports.

He also said that palace officials denied him access to cover the third day of Charles' Welsh tour in July when he visited the Royal Mint in Glamorgan.

A source claimed: "Bower asked permission in advance, but about two days before, they said it was full. Bower couldn't believe they didn't have space for one person behind a rope."

The palace insinuate it was nothing personal, with a spokesman stating: "Bower was offered alternative engagements to visit – owing to there not being a space on that one occasion – which he declined."

princess diana best looks
A young Diana relaxes with Prince Charles in a loose pink dress and matching hat with bow detail during their first official Australian tour together in 1983. Getty

The source added that the book is one of a kind, adding: "Until now all the books about Charles have been pretty reverential. They have all sought to get his approval. This treats him as a story, not as an object to be glorified."

It will cover the heir's "politics and his attitude towards his family" as well as how he tried to overhaul his image following Princess Diana's death in 1997.

Royal insiders are dubious about the book and The Mirror's royal correspondent Victoria Murphy believes Charles could mount a legal battle to prevent its publication.

The Prince has not welcomed any book that threatens to "rock the stability he has enjoyed in recent years," she said, according to The Express.

Bower's book Sweet Revenge, published in 2012, revealed music mogul Cowell's affair with popstar Minogue. It also told how Cowell planned to seduce Minogue's friend, singer Natalie Imbruglia, a year later by inviting her on to his yacht.

Rebel Prince: The Power, Passion and Defiance of Prince Charles will be published on 22nd March in hardback retailing at £20, ahead of the His Royal Highness The Prince of Wales' 70th birthday in November.

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