Harry and William's 'devastating' relationship breakdown revealed in new book

An infamous royal author, Robert Lacey, has been left "astonished" by what he found out when writing a new book about the relationship between Prince William and Harry.

Lacey, who also works as a historical consultant to the hit Netflix series The Crown, is set to release the new book titled Battle Of Brothers: William And Harry –­ The Friendship And The Feuds in October.

The book is said to address "the unique and complex relationship at the heart of the royal family's recent woes," People magazine reported.

Lacey's book also puts the brothers' relationship in historical context, exploring the bond between "heir" and the "spare" over the years.

"Much reported on but little understood, Diana's boys have lived under constant scrutiny since birth," reads the book's synopsis, as revealed by People.

"Raised to be the closest of brothers, the last 18 months have been a devastating breakdown of their once unbreakable bond," it said. "With an unrivalled knowledge of court life and access to impeccable sources, Robert Lacey investigates the untold reality of the brothers' relationship, explaining what happened when two sons were raised for vastly different futures and showing how the seeds of damage were sown as their parents' marriage unravelled."

William was said to be worried about Harry and Meghan's fast-paced relationship. Photo / Getty Images

According to People, the book also looks into how the relationship between the siblings has been impacted by their marriages to Kate Middleton and Meghan Markle. It also includes the changing dynamic of Harry stepping back as a senior royal the move to Los Angeles with son Archie.

"I have been astonished and sometimes moved to tears by the fresh details and insights I have discovered in researching this story of family conflict," Lacey said. "It has been both enthralling and painful to trace this drama through the memories of close witnesses and some of the people most intimately involved."

"These two brothers –­ once inseparable and now separated by much more than mere distance –­ have been acting out the contradictions that go back into their childhoods and even before that – into their parents' ill-fated marriage," he added.

"We have seen conflicts between heir and spare in every recent generation of the royal family, but nothing so profound as this."

Rumours of an alleged royal feud came to light in 2019, when British author Katie Nicholl claimed William was growing increasingly worried for his brother and whirlwind romance with Meghan Markle.

"William was quite concerned that the relationship had moved so quickly," Nicholl claimed in the TLC documentary Kate V. Meghan: Princesses At War?

Prince Harry also hinted at a past rift with his older brother in the 2019 ITV documentary Harry & Meghan: An African Journey.

"Part of this role and part of this job, this family, being under the pressure that it's under, inevitably stuff happens," he shared.

"But look, we're brothers, we'll always be brothers. We're certainly on different paths at the moment but I'll always be there for him and I know he'll always be there for me."