Biographer Robert Lacey will address “the unique and complex relationship at the heart of the royal family’s recent woes” in his upcoming book, Battle of Brothers: William and Harry — the Friendship and the Feuds.

According to a press release on Saturday, the book, which is set to be released in October, will also put the two brother’s relationship into a historical context, detailing how the “heir” and the “spare” dynamic worked out across generations.

“Much reported on but little understood, Diana’s boys have lived under constant scrutiny since birth. 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.

“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 unraveled [sic].”

The book will also address how their wives Kate Middleton and Meghan Markle made an impact on the brothers’ relationship, as well as to bring to light the reason why Harry and Meghan stepped back as senior royals and moved to Los Angeles with their son Archie.

Lacey expressed how he has been “astonished” by some of what he has uncovered while working on the project.

“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. 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,” he said.

“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.”