A new book is making some shocking claims about how Prince Harry’s relationship with Meghan Markle led to friction with other members of the royal family, particularly his brother, Prince William.

According to a report in Page Six about Christopher Andersen’s upcoming book Brothers And Wives: Inside The Private Lives of William, Kate, Harry And Meghan, the tension between the two brothers came to a head when Harry told William he was going to propose to the “Suits” actress.

William’s response, claims the book, was to ask, “Why rush things?” This reportedly infuriated Harry, who fired back, “Who the hell do you think you are?”

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The brothers’ relationship deteriorated further when William enlisted their uncle, Earl Spencer — brother of the late Princess Diana — to encourage Harry to take things more slowly.

This, however, made “matters far worse,” causing Harry to become “furious that his brother was actively seeking to have others interfere in his personal affairs.”

Before long, Harry became “angry” with anyone he felt was “against Meghan.”

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In the book, Andersen writes that William and wife Kate “wanted a proper English rose” for Harry, and became increasingly “alarmed” by the scandalous headlines surrounding Meghan’s father, Thomas Markle, and her estranged half-siblings, Samantha and Thomas Jr.

As time went by, the relationship between William and Harry became increasingly strained. “It feels like I have lost my best friend,” William reportedly said, even telling their father, Prince Charles, that Harry’s obsession with Meghan was “like something I’d never seen.”

READ MORE: Prince Charles ‘Shellshocked’ Over Prince William And Prince Harry’s Alleged Fallout

ET Canada has reached out to the royals’ reps for comment.