The book, Endgame, is set to be released on Tuesday and will look “inside” the royal family and the monarchy’s “fight for survival”.
Scobie has previously been dubbed the Duke and Duchess of Sussex’s “mouthpiece” for his sympathetic portrayal of the couple but has insisted that he is “not their friend”.
He is also said to claim that the King is jealous of William’s position and resented Harry’s popularity with the media.
It is also alleged that the Princess of Wales and Meghan were encouraged to dress like Princess Diana so that some of her shine would “rub off on them”, with Kate “portrayed as a woman terrified to do anything more than grinning photo ops”.
Buckingham Palace and Kensington Palace declined to comment on the book on Monday.
However, those close to William were said to be “exasperated” by its tone. A senior royal source told the Evening Standard: “This is all about bolstering his sales. The truth is the Prince of Wales has always been circumspect and discreet when asked about his family.”
In Endgame, William is portrayed as a hotheaded man, determined to lead the royals his way. Scobie claims the prince wants to “rip up” the rulebook and do things “the Cambridge Way”.
Scobie, 42, previously co-authored the book Finding Freedom — a biography of the Sussexes and their split from the royal family.
He has moved to quash claims from critics that he is a “mouthpiece” for the Sussexes, tweeting of his latest book: “It’s not ‘Harry and Meghan’s book’, I’m not ‘Meg’s pal’, the Sussexes have nothing to do with it. Their story is a small part of a much bigger one.”