Royal Writer Omid Scobie ripped into 'hot-headed' Prince William in an extraordinary interview with French magazine Paris Match.
The Sussexes' cheerleader accused the Prince, 41, of being in 'heir-mode' and driving the rift with his brother Harry.
It came after the author, 42, insisted he was not on the Sussexes' payroll ahead of the release of his new book Endgame.
Paris Match released extracts from Endgame yesterday, alongside an interview with Omid.
He said William is a 'hot-headed' company man who is 'increasingly comfortable with the Palace's dirty tricks and the courtiers who dream them up'.
Omid Scobie, pictured, ripped into 'hot-headed' Prince William in an extraordinary interview with French magazine Paris Match
The Sussexes' cheerleader accused the Prince, 41, of being in 'heir-mode' and driving the rift with his brother Harry
Omid, who was the royal executive editor of Yahoo! News until July of this year, claimed it is William who, through his loyal aides and press relationships, has painted his brother as mentally fragile.
The author claimed: 'The side of it that a lot of people don't know, or within our industry have known but chosen not to report, is just how involved William has been in many of the things that have gone out about his own brother.'
The Prince 'knows his father's reign is only transitional,' Scobie wrote, 'and is acting accordingly.'
In another painful chapter in the 400-page book, Omid alleged that William ignored Harry's texts when the family were racing to reach Queen Elizabeth II in Balmoral in her final hours on September 8, 2022.
Harry allegedly paid to charter a flight alone from Luton Airport to Aberdeen for £30,000. Omid said he found out his grandmother had died when a BBC News alert pinged on his phone.
Omid also claimed King Charles was 'cautious' when talking to Prince Harry after the publication of Spare and family members were told not to trust him.
The author described an alleged conversation between Charles and his son Harry, who had apparently called to talk to him about his vitriolic memoir following its release in January.
He said the King was 'cautious', further claiming that a message was circulated among family members not to trust Harry with anything and to ignore both the book's claims and what he was saying to promote it.
The Prince 'knows his father's reign is only transitional,' Scobie wrote , 'and is acting accordingly.'
King Charles - right - was said to be 'cautious' after speaking to Prince Harry after the publication of Spare. They are pictured at Westminster Abbey in 2019
He says the King was 'cautious', further claiming that a message was circulated among family members not to trust Harry with anything. The royals are pictured on November 11
Spare became the fastest selling non-fiction book in the UK since records began in 1998, and sold 3.2million copies worldwide in the first week of publication
The journal reported that a source close saying of Charles' approach to the conversation: 'He wanted to limit their discussion to a harmless exchange.
'Concerning Harry, the message that circulated in the family was not to trust him... everyone took it very seriously.'
Harry used Spare to make a series of personal attacks on his family, including the claim they helped 'trash' his and Meghan's reputations, forcing them to move to California, and have 'shown no willingness to reconcile'.
He also accused his elder brother of physically attacking him at Nottingham Cottage in 2019 and 'lunging' at him after the Duke of Edinburgh's funeral in 2021.
In Endgame, Scobie says that despite the strained relationship between Charles and the Sussexes, she and Harry still keep him 'up to date' by 'sending him photos of their children'.
But he claims that after Harry and Meghan sent the Waleses' three children gifts last Christmas, William and Kate did not respond with so much as a text.
The author – dubbed 'Meghan's mouthpiece' – repeats previous claims that the Duchess of Sussex 'never wants to set foot in England again', 'never felt at home' in the UK and 'never wants to be involved in the British monarchy again'.
Yet he says Harry has said he is 'ready to forget' the recent troubles with his family and has given up on getting the 'apology or explanation' he has previously demanded, quoting the prince as saying: 'At this point, who cares, right?'
The claims emerged yesterday in Paris Match magazine to publicise Scobie's second royal tome, Endgame: Inside the Royal Family and the Monarchy's Fight for Survival.
His first was Finding Freedom, the rabidly pro-Sussex account of Harry and Meghan's romance, wedding and decision to acrimoniously quit as working royals.
The article in Paris Match, ahead of the book's publication on Tuesday, is a tangled mass of quotes from it, combined with Scobie's own opinions on the state of the Royal Family and seemingly the interpretation of the magazine's journalist.
In Endgame, Scobie says that despite the strained relationship between Charles and the Sussexes, she and Harry still send him photos of their children. Pic: Charles on Nov 21
Scobie claims there was 'palpable silence' as the former 'Fab Four' travelled the short distance to Windsor's Long Walk for a royal walkabout in 2022 (pictured)
Several new claims are made but none is obviously explosive – so far – although Scobie has conducted several pre-publication interviews to be aired over the next few days, and there is no doubt that the Palace views his public vendetta with the Royal Family as unhelpful.
Many insiders point out that it is no surprise Kate and Meghan have not been in 'direct communication' for four years, as Scobie describes it, because the Sussexes left for Canada with baby Archie in the autumn of 2019 and the duchess has returned to the UK, briefly, only four times since.
Paris Match adds that Kate 'immediately detected a rival to her' in Meghan, writing: 'She spent more time talking about Meghan… than with Meghan,' according to 'a close friend of the couple'.
Harry, while promoting his tell-all memoir earlier this year, said it quickly became 'Meghan versus Kate' after he started dating the US TV actress in 2016.
Harry also repeated claims that Kate made Meghan cry during a row about bridesmaids' dresses ahead of the Sussexes' 2018 wedding.
William, Kate, Harry and Meghan were at one time dubbed the Royal Family's 'Fab Four' after they initially appeared to form a close bond. But when they were reunited for a car journey the day after the Queen's death in September 2022, there was a 'palpable' silence as they travelled the short distance to Windsor's Long Walk, the book claims.
The magazine goes on to say the book describes the complete breakdown of relations between the brothers, saying: 'Not even a text message at Christmas, although, according to Scobie, Meghan and Harry had sent gifts to Kate and William's children.'
While neither Buckingham Palace nor Kensington Palace wants to comment on the claims, the book's publication is unlikely to do anything to bolster hopes that Harry may one day be reconciled with his family.
In Endgame, Scobie suggests William and Harry's relationship is beyond repair because the Prince of Wales sees his brother as a 'defector'
Last week it was suggested there was a thawing of relations after sources close to the prince leaked to chosen media that he had a warm conversation with his father when he rang to wish him a happy 75th birthday.
Scobie insists he is not friends with the Sussexes, nor was he in direct contact with them over the book, and the Sussexes have denied they are 'affiliated' with it.
But there is a certain level of detail that, if true, could only have come from sources who are extremely close to the couple.
This includes claims that Harry twice texted his estranged brother around the death of the Queen, and heard nothing back, and that his father, King Charles, called him from an 'unknown number'.
Paris Match also reports that Scobie will say it was Harry's aunt, Princess Anne, who persuaded Charles to withdraw the use of Frogmore Cottage from the Sussexes, prompting the prince to plead: 'Don't you want to see your grandchildren any more?'
And Scobie says that only Harry's uncle, Prince Edward, was concerned about the prince's mental health.
He even accuses the King of being more worried about the pressure on Prince Andrew in the wake of the Epstein scandal.
The magazine says: 'Meanwhile, the King could not bring himself to hurt his brother. [He] was in tears because he was afraid for Andrew's mental health. Charles leads with his head and his heart. William is colder. He wants the job done and he had no problem with casualties along the way.'
There are clear howlers in the extracts from the book that have been released, including the suggestion the Prince of Wales 'is eager to ascend the throne'.
Friends of William have made clear that he wants to ring-fence his three young children for as long as possible and has no desire to hasten his progress towards becoming king.
MailOnline have approached Buckingham Palace for a comment.