Prince Harry was allegedly so enraged by Prince William questioning his whirlwind romance with Meghan Markle that he blurted out to his older brother, "Who the hell do you think you are?"

The allegation was made by bestselling author Christopher Andersen in his new book being released on Tuesday titled "Brothers and Wives: Inside the Private Lives of William, Kate, Harry, and Meghan."

In it, Andersen quoted a source who claimed the outburst occurred in September 2017 when Harry, 37, hinted he was going to propose to his American girlfriend, Page Six reported on Monday. William, who is second in line to the throne, then asked his sibling "Why rush things?"

According to the outlet, Andersen wrote that Harry was also "furious that his brother was actively seeking to have others interfere in his personal affairs." William, 39, allegedly reached out to their uncle, Earl Charles Spencer, and expressed his concerns about Harry’s relationship moving quickly. Andersen noted that William, who can be "very stiff," allegedly feared that the former American actress was "an opportunist."

PRINCE HARRY FELT HE WAS ‘BEING ERASED FROM THE FAMILY’ AFTER QUEEN ELIZABETH’S PHOTO SNUB, BOOK CLAIMS

Prince Harry Prince William

Prince Harry (left) and Prince William's (right) alleged fallout is explored in Christopher Andersen's new book. (Getty)

Andersen also revealed that both William and his wife, Kate Middleton, were "alarmed" by the numerous tell-alls that Markle’s estranged father, half-sister and half-brother gave to the tabloids.

A horrified William allegedly told a confidant, "I don’t know what to believe." He even told his father Prince Charles that Harry’s relationship with Markle was "like something I’d never seen" and "it feels like I have lost my best friend."

William had a lengthier courtship with Middleton, 39. They were together for eight years before they tied the knot in 2011. Harry and Markle, 40, met on a blind date in 2016 and announced their engagement in 2017.

Reps for Kensington Palace, as well as the Duke and Duchess of Sussex, didn’t immediately respond to Fox News’ request for comment.

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Prince William Kate Middleton 10 year anniversary photos

Prince William and Kate Middleton had a lengthy courtship before they tied the knot. (Chris Floyd/Camera Press/PA via AP)

Andersen has made several bombshell allegations in his book. He claimed that Queen Elizabeth II had a palace aide move a portrait of the Duke and Duchess of Sussex and their son Archie, who was eight months at the time, off-camera before she recorded her 2019 holiday broadcast, Page Six reported.

The insider alleged that the 95-year-old "looked over the tables where the photographs she had so lovingly selected were arranged."

"All were fine but one, [the queen] told the director," the source alleged. "Then she pointed to the Sussex picture and said: ‘That one, I suppose we don’t need that one.’"

The queen’s alleged holiday decision came after Harry, 37, chose to spend Christmas with his mother-in-law Doria Ragland alongside his wife and their son in Canada instead of the UK, the outlet reported.

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Queen Elizabeth Holiday

Queen Elizabeth II records her annual Christmas broadcast in Windsor Castle, Berkshire, England. Circa 2019. (Photo by Steve Parsons - WPA Pool/Getty Images)

William was allegedly "aghast" when he saw the photo in question missing from the lineup. The source alleged that the prince told Middleton that his sibling was likely to be "terribly upset."

Following the broadcast, Harry allegedly told a pal that he "felt as if he, Meghan and Archie were being erased from the family."

In January 2020, the Duke and Duchess of Sussex announced they were stepping back as senior members of the royal family. Their departures from royal duties began that year over what they described as the British media’s intrusions and racist attitudes towards the former "Suits" star.

A spokesperson for the queen told Fox News that "we never comment on these sort of books."

PRINCE CHARLES WAS THE ROYAL WHO ASKED ABOUT COMPLEXION OF MEGHAN MARKLE, PRINCE HARRY'S FIRSTBORN, BOOK SAYS

Meghan Markle

Meghan Markle, an American actress, became the Duchess of Sussex when she married Britain's Prince Harry. (Photo by Getty       )

Andersen also alleged that Charles was the royal who speculated about Archie’s skin tone before he was born.

In March 2020, the Duke and Duchess of Sussex sat down for a tell-all interview with Oprah Winfrey during which they made shocking allegations about their time in the royal family. One of the most provocative claims was when Markle revealed a member of the royal family had "concerns" about the color of her child’s skin before he was born. At the time, Harry made sure to note that it was not the queen nor Prince Philip, leaving the door open to speculation.

A source close to the royal family alleged to Andersen that Charles wondered aloud about the child’s complexion during a conversation in 2017 that took place shortly after the Duke and Duchess of Sussex got engaged.

"I wonder what the children will look like?" the 73-year-old reportedly told his wife, Camilla, as quoted by Page Six.

QUEEN ELIZABETH ONLY PICKS UP THE PHONE FOR THESE TWO PEOPLE, ROYAL EXPERT SAYS

Prince Harry Meghan Markle Oprah Winfrey interview

This image provided by Harpo Productions shows Prince Harry, from left, and Meghan, The Duchess of Sussex, in conversation with Oprah Winfrey. (AP)

Camilla was reportedly "somewhat taken aback" and noted that the child would be "gorgeous."

Allegedly lowering his voice, Charles asked: "I mean, what do you think their children’s complexion might be?"

Representatives for Clarence House didn't immediately respond to Fox News’ request for comment. However, a spokesperson told The New York Post that "this is fiction and not worth further comment."

The book claimed that Charles was merely voicing an innocuous curiosity about what the child might look like, implying that it was more of a public relations issue of the royal family dealing with a darker-skinned member. The outlet reported that Charles’ musings were quickly twisted by courtiers and given a much more toxic and racist spin by the time Markle and Harry heard about them.

PRINCE HARRY HONORS VETERANS AT 2021 SALUTE TO FREEDOM GALA: ‘THE MILITARY MADE ME WHO I AM TODAY’

Prince Charles

Prince Charles was allegedly heartbroken after Prince Harry spoke out in a televised interview with Oprah Winfrey. (Getty          )

Nick Bullen, an award-winning documentarian as well as the co-founder and editor-in-chief of True Royalty TV, previously told Fox News that he believes Charles is "heartbroken" over the allegations. The filmmaker has worked closely with the Prince of Wales for nearly a decade.

"I think the Prince of Wales must be shocked and heartbroken," Bullen told Fox News last year. "Imagine if any member of your family, especially your son or daughter, goes on television and says, ‘My relationship has broken down with my father?’ Even if it’s true, the world now knows. So I think the Prince of Wales must be heartbroken."

"I have no doubt in my mind the man cares about his son," Bullen added. "We’ve only really heard one side of the story. And so far, Meghan and Harry have won the PR war."

Shortly after the interview aired, Buckingham Palace issued a 60-word statement on behalf of the queen.

PRINCE HARRY SAYS ‘MEGXIT’ IS ‘A MISOGYNISTIC TERM CREATED BY A TROLL’ TO TARGET HIS WIFE

Prince Harry Meghan Markle

The Duke and Duchess of Sussex reside in California with their two children. (Photo by John Lamparski/Getty Images)

"The whole family is saddened to learn the full extent of how challenging the last few years have been for Harry and Meghan," the statement said.

"The issues raised, particularly that of race, are concerning," the statement added. "While some recollections may vary, they are taken very seriously and will be addressed by the family privately. Harry, Meghan and Archie will always be much loved family members."

The Duke and Duchess of Sussex now reside in the coastal city of Montecito, California. On June 4, the couple welcomed their second child, a daughter named Lilibet "Lili" Diana Mountbatten-Windsor. The name pays tribute to both the queen, whose family nickname is Lilibet and his late mother, Princess Diana.

Fox News' Tyler McCarthy and The Associated Press contributed to this report.