The rift between Prince William and Prince Harry is the most “profound” among the recent generation of the royal family, royal author Robert Lacey said.

The biographer, who serves as a historical consultant for the Netflix series The Crown, is set to release the book Battle of Brothers: William and Harry – the Friendships and Feuds in October.

“Raised to be the closest of brothers, the last 18 months has seen a devastating breakdown of their once unbreakable bond,” the book’s synopsis reads.

In the book, Lacey explains “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”.

Lacey said he had been “astonished” by the information he had uncovered for the book.

“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,” he said in a press release.

“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.

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

In the 2019 documentary Harry & Meghan: An African Journey, the Duke of Sussex shared a glimpse into his relationship with his older brother.

“Part of this role and part of this job, this family, being under the pressure that it’s under, inevitably stuff happens,” he said. “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.” 

Another book on royals, Finding Freedom: Harry and Meghan and the Making of a Modern Royal Family, will be released in August. The biography, authored by journalists Omid Scobie and Carolyn Durnad, promises to go “beyond the headlines to reveal unknown details of Harry and Meghan’s life together, dispelling the many rumours and misconceptions that plague the couple on both sides of the pond”.

This article originally appeared on Over60.