Prince Harry and Prince William's Fallout Has Left Prince Charles 'Shellshocked,' Says Source

The sustained tensions between Prince William and Prince Harry have devastated many members of the royal family - including their father, Prince Charles.

The future monarch, 72, has historically had complicated relationships with his sons and is finding it hard to intervene as increasingly painful revelations about the roots of the brothers' discord continue to come to light.

Charles is "shellshocked by it all," a friend tells PEOPLE exclusively in this week's issue. "He is very hurt and upset [by the ongoing fallout]."

The latest exploration of the deepening fracture between the princes comes via additional chapters in royal historian Robert Lacey's Battle of Brothers: William, Harry and the Inside Story of a Family in Tumult.

As PEOPLE previously reported, the schism between the brothers began when William expressed concern about the speed at which Harry's relationship with then-girlfriend Meghan Markle was moving prior to their May 2018 wedding.

According to Lacey's new chapters, things worsened again in October 2018 when William, 39, learned of allegations from staffers who said they had been bullied. (When the bullying claims first surfaced in The Times in March, the Duchess of Sussex's office strongly denied the allegations and said they were part of a smear campaign against the Duchess, 39. The palace set up an independent inquiry, which is still "ongoing," a source confirms.)

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Harry, 36, was appalled by what he viewed as baseless allegations against his new wife, and was "equally furious" that his brother would give the claims credence, Lacey writes. (Representatives for both brothers have declined to comment.)

Reconciliation between the brothers has been made more difficult by geographic distance and the challenges of the pandemic. Reunited for the first time in more than a year at the April 17 funeral for their grandfather Prince Philip, they shared a brief public chat outside St. George's Chapel.

"Everyone was optimistic," a source close to the royal household tells PEPOLE, "but nothing really happened."

Adds another close source: "There was not really any time to build bridges."

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But there is another reunion just around the corner - on July 1, both brothers are expected to attend the unveiling of the long-awaited statue of their mother, Princess Diana, at Kensington Palace Gardens, a project they commissioned together several years ago.