Prince William briefed the press about Prince Harry, author claims in new book

Prince William briefed the press about his younger brother Prince Harry amid the ongoing rift between the two brothers, according to a new book about Britain's royal family.

In his new book "Endgame," author Omid Scobie, also an ABC News royal contributor, claims that William's alleged press briefing is among the things that have caused "irreparable damage" between William and Harry, the only children of King Charles III and the late Princess Diana.

"He's sharing private information about his brother that ended up on the front page of a newspaper not long later," Scobie told ABC News' Maggie Rulli in an interview, an excerpt of which aired Monday on "Good Morning America." "And these are things that have caused irreparable damage in the relations between each other."

Scobie said that in his view, William has become a "company man" within the royal family. When Charles became king last year, William, as the eldest son, rose to first in line to the throne.

"We've seen the kind of emergence of a man who is much harder, who seems to have embraced and embodied the royal institution," Scobie said of the 41-year-old father-of-three.

While the public long saw William and Harry, 39, as brothers bonded by both their roles in the royal family and the loss of their beloved mother, the brothers have, in reality, faced a long disintegrating relationship.

Since stepping down from his role as a senior royal and moving to the United States with this family, Harry, fifth in line to the throne, has spoken publicly about his rift with his brother, details of which he also shared in his bestselling memoir, "Spare."

Scobie's book, "Endgame," which goes on sale Tuesday, details the aftermath of Harry and his wife Meghan, the Duchess of Sussex's decision to exit the royal family.

Scobie writes that one explosive claim Harry and Meghan made after leaving her senior royal role -- when they told Oprah Winfrey that royal family members had conversations with Harry about "how dark" their son's skin might be -- led to a follow up conversation with Charles.

Scobie alleges it was two people who raised questions about their son's skin tone. He told Rulli that he knows the names of the two people but that U.K. law prevents him from publicly revealing their names.

"The names were mentioned in letters between Meghan and Charles that were exchanged sometime after the Oprah [Winfrey] interview," Scobie said. "We know from sources that Charles was horrified that that's how Meghan felt those conversations were, and that he wanted to, sort of as a representative of his family, have that conversation with her."

Scobie continued, "And it's why I personally think that they have been able to move forward with some kind of line of communication afterwards, though they may not see eye-to-eye on it."

Scobie also looks in "Endgame" at the future of Britain's royal family, which he describes as being at a "crossroads" since the death of Queen Elizabeth II in September 2022.

"I think before people assume that I'm calling this the end of the royal family, I'm simply declaring that we've reached a sort of pinnacle moment where the royal family, as we know it, is at," he said.

Scobie said that his book, which has generated headlines even before its release, contains details that the royal institution "won't necessarily want to hear."

"To shine a light in the darkest places, one has to ruffle feathers," Scobie said. "One has to do things and write things that I know the palace won't necessarily want to hear."

Both Buckingham Palace and Kensington Palace declined to comment on Scobie's book to ABC News.

A spokesperson for the Sussexes has not yet responded to ABC News' request for comment.