In a new book titled "Endgame," author and ABC News royal contributor Omid Scobie sheds light on the ongoing rift between Prince William and Prince Harry, providing insights into the alleged actions that have led to "irreparable damage" in their relationship. The book delves into the dynamics within Britain's royal family, including William's supposed press briefing about his younger brother.

According to Scobie, William's briefing with the press resulted in the disclosure of private information about Harry, which eventually made headlines. In an interview excerpt aired on "Good Morning America," Scobie pointed out that these actions have only deepened the divide between the two siblings.

Scobie further suggests that William has transformed into a "company man" within the royal family, particularly since his rise to first in line to the throne following King Charles III's ascension last year. The author describes the 41-year-old father-of-three as someone who has embraced and embodied the royal institution, becoming markedly more firm in his demeanor.

Despite the public perception of a close bond between William and Harry, who have both faced the loss of their mother, Princess Diana, their relationship has reportedly been deteriorating for some time. This rift became more evident after Harry stepped down from his role as a senior royal and relocated to the United States with his family. The younger prince has publicly discussed the tensions with his brother and even detailed them in his bestselling memoir, "Spare."

Scobie's "Endgame," set to be released on Tuesday, examines the aftermath of Harry and his wife Meghan's decision to exit the royal family. The author highlights a particular claim made by the couple during their interview with Oprah Winfrey, where they alleged that members of the royal family had discussions concerning the potential skin tone of their son.

Divulging more details from his book, Scobie reveals that Harry and Meghan mentioned the names of the individuals involved in these conversations in letters exchanged with Charles after the interview. However, due to U.K. law, Scobie refrains from publicly revealing the names. He explains that Charles was horrified by how Meghan perceived the discussions and felt the need to have a conversation with her on behalf of the family.

"Endgame" also explores the future of the British royal family, which Scobie describes as standing at a "crossroads" since the passing of Queen Elizabeth II in September 2022. The author clarifies that he is not declaring the end of the royal family, but instead highlighting this pivotal moment in its history.

Scobie acknowledges that his book contains information that the royal institution may not want to hear, as he aims to uncover hidden truths. Both Buckingham Palace and Kensington Palace have declined to comment on the revelations in Scobie's book, while a spokesperson for the Sussexes has not yet responded to requests for comment from ABC News.