Royal historian Robert Lacey has written a new book on what he calls the "battle" between William and Harry

Prince Harry, Duke of Sussex and Prince William, Duke of Cambridge
Prince Harry and Prince William
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The rift between Prince William and Prince Harry and the events leading up to Harry's departure from the royal family alongside his wife Meghan Markle are laid bare in a revealing new biography by a top royal historian.

Robert Lacey, who has penned books on the princes' mother, Princess Diana, and  Queen Elizabeth has turned his forensic microscope onto the schism that has rocked the monarchy.

An excerpt from Battle of Brothers: William & Harry – The Inside Story of a Family in Tumult, serialized by the Daily Mail late Friday, explores the months leading up to Harry and Meghan's departure from the royal family and the negotiations that took place at the so-called Sandringham summit.

Of the royal family summit in January, Lacey, who is also a historical consultant on Netflix’s The Crown, writes, "The Queen concluded that the four of them — Harry, William, Charles and herself — should sit down with their respective private secretaries at Sandringham the following Monday to hash things out, though William confided to a friend that he would much rather leave all the haggling to the staff.

" 'I put my arm around my brother all our lives,' " William said, according to the new book, " 'and I can’t do it anymore. We’re separate entities.' "

Lacey writes: "William maintained his distance for the Sandringham summit. The Queen had suggested the family should gather for lunch before their big pow-wow in the library that afternoon, but he refused his grandmother’s invitation."

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Prince William and Prince Harry in 2017
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Of the negotiations, Lacey writes, "'It was like dealing with a hard-nosed Hollywood lawyer,’ says a senior palace source familiar with the negotiations. ‘The Sussexes wanted guarantees on every single point as if it were a contractual negotiation.’

"They totally misplayed the negotiations," says a palace insider in the book, "But then so did the palace."

"The Queen deliberated for several weeks, then ruled that Harry and Meghan could not use Sussex Royal as the brand name to market their merchandise and various activities in North America," the excerpt in the Daily Mail continues.

"It was reliably reported that Her Majesty remained well-disposed towards her grandson and granddaughter-in-law. She wished them well in their new life in Canada — and her ‘eighth great-grandchild’ as well, of course," the excerpt says.

"But it was also said by those in the know that the couple’s erratic and impulsive behavior for the past year had not inclined Queen Elizabeth II to entrust the Sussexes with the use of the word ‘royal’ any time soon."

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Prince William, Kate Middleton, Prince Harry and Meghan Markle in March 2020
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Tensions within the royal family were evident at the time of the Queen's 2019 Christmas broadcast — namely the absence of a photo of Meghan, Harry and baby Archie.

"It was unheard of for the royal Christmas desk not to feature a cozy image of the latest royal grandchild or great-grandchild. But in 2019 there was no sight of Harry and Meghan’s six-month-old son, Archie," Lacey writes in the Daily Mail's excerpt.

"The new royal picture that the Queen did release on January 3 to mark the new decade showed Queen Elizabeth II herself, the future King Charles III, the future King William V — and, going even further, King George VII in the shape of little Prince George, just coming up to seven years old," he continues.

"According to insiders, this formal photograph, taken in the Buckingham Palace Throne Room a week before Christmas 2019, was the idea of Prince Charles, anxious to promote his cause of the ‘slimmed-down monarchy.’

"Palace sources have also let it be known that the plan of depicting the direct line of royal succession was enthusiastically supported by Prince William, which might be seen as sending his younger brother a message.

"The message was received and it was taken to heart."

Prince Harry, Prince William, Prince Charles
The royal family in March 2020
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In an interview with the Daily Mail on Friday, Lacey is careful not to take sides and acknowledges there are difficulties on both sides, but adds “the palace got it wrong” with Harry and Meghan.

“They always treat the second-born badly, not to say cruelly. It happened with Princess Margaret. It happened with Prince Andrew. They just don’t know what to do with the spare," he says.

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Harry, he adds, realized “there was something rotten at the heart of royalness that is not for him.”

Lacey hopes that “there is still time to act” for the brothers' father Prince Charles to nurture a proper reconciliation.

Battle of Brothers, which will be released Oct. 20 in the U.S. by Harper, is the second bombshell book to largely feature the brothers' split, following Finding Freedom, which was released in August.