Nicholas Witchell: Prince Charles' main concern is to safeguard the feelings of Princes William and Harry

Rosa Monckton has described as "cruel, spiteful and hurtful" allegations made about the princess in Penny Junor's book, Charles: Victim or Villain? which goes on sale to coincide with the prince's 50th birthday next month.

Diana: Alleged to be the first to commit adultery

Her comments come after sharp denials of involvement by Charles and his long-term companion Camilla Parker-Bowles.

Buckingham Palace also angrily denounced certain claims and issued a plea to "let Diana be" for the sake of princes William and Harry.

The Duchess of York, Sarah Ferguson, also described the book as a "shameful and chilling attack, from which she can no longer defend herself".

Speaking to BBC One's Six O'Clock News, Ms Monckton said: "I haven't read the book, but I'm aware of one or two of the allegations and I think they're cruel, spiteful and hurtful to those who loved her.

Rosa Monckton: "I don't think Prince Charles was involved"

"Perhaps a bit of sensation was necessary to justify the vast fee I understand Ms Junor has earned from this book. I think a lot of it is just re-heated gossip.

"I don't think for a moment that Prince Charles was involved. He has never involved himself in any of the allegations and counter-allegations about his marriage and I don't believe he would start now because his main aim must surely be to protect his boys.

"What I find difficult is the fact that the princess was almost canonised after her death and now the coin has been flipped and all these awful lies and untruths are appearing."

Ms Junor defended her book saying it is meant "to explain what really happened in that marriage" between Charles and Diana.

Penny Junor: Book hopes to explain Royal marriage

The book claims that Diana was the first to commit adultery, with her bodyguard Barry Mannakee, who is now dead.

The Queen is accused of being reluctant to allow a royal aircraft to fly Diana's body home after the crash that killed her in Paris last year.

Ms Junor also alleges that Diana made death threats to Mrs Parker-Bowles and that the Royal Family rowed with Diana's family, the Spencers, about funeral arrangements.

Officials have rejected reports that there was a "crisis summit" at Buckingham Palace to discuss the contents of the book.