Since Meghan Markle entered the sphere of the royal family, rumors have swirled of tension between Prince Harry and Prince William over the relationship.

It was reported earlier this year that William, 38, cautioned Harry, 36, against moving too quickly in his relationship with Markle, 39, which is said to have contributed to an alleged rift between the brothers.

Now, "Battle of Brothers: The Inside Story of a Family in Tumult" author Robert Lacey is backing up similar claims in an excerpt from the book obtained by People magazine.

"The fundamental conflict was between the two males who had known each other all their lives and had never hesitated to tell each other exactly what they thought and felt," read the passage.

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Britain's Prince Harry (left) and older brother Prince William. A rift reportedly developed between the two after Harry began to accelerate his relationship with Meghan Markle.

Britain's Prince Harry (left) and older brother Prince William. A rift reportedly developed between the two after Harry began to accelerate his relationship with Meghan Markle. (Photo by Tolga Akmen - WPA Pool / Getty Images)

He added: "William worried that his brother was moving too fast in his courtship — and he did not shrink from saying as much when Harry started talking about getting hitched to Meghan quite soon."

The author claimed that a "confrontation" occurred between the royals in "late 2016 or early 2017" in regards to Harry's desire to marry Markle.

"William couched his question in terms of apparent concern for Meghan," Lacey wrote.

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“'Waity William,' of course, took so long to commit to Kate [Middleton] for the sake of the monarchy. He had been auditioning her for a job all those years. So Harry could not help but wonder whether Will was really concerned about his personal happiness — or whether he was, once again and as per usual, thinking about the makeup and fortunes of 'the Firm' whose boss he would become one day?" said the author, per People. "The response from Harry was a brusque and offended pushback."

Prince Harry (left) and Meghan Markle (right) have relocated to California after stepping back as senior members of the royal family. 

Prince Harry (left) and Meghan Markle (right) have relocated to California after stepping back as senior members of the royal family.  (Karwai Tang/WireImage via Getty)

After Harry and Markle wed in 2018, it seemed that he would work alongside his brother and his wife, Kate Middleton, but it soon became clear that would not be the case.

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"Here we have a couple of brothers who loved each other dearly — most profoundly and genuinely, in fact — but who could give as good as they got when it came to a clash over something that mattered intensely to them," wrote the historian. "For William it was the future state of his monarchy — his sacred trust; while for Harry it was the love of the complex and captivating woman who had finally made sense of his life."