It’s no secret that King Charles and Princess Diana’s seemingly storybook romance turned out to be a nightmare – but one author claims things were much darker behind closed doors.

Christopher Andersen has written a new book about Queen Elizabeth II’s eldest son titled "The King: The Life of Charles III." He spoke to numerous palace insiders, as well as those who’ve known the former Prince of Wales or worked with him closely over the years. His goal was to further investigate the 74-year-old’s "lonely" childhood and military training, as well as several scandals surrounding his relationships that rocked the House of Windsor.

Andersen alleged to Fox News Digital that the marriage between Charles and Diana became so volatile that royal protection officers were wary of all the weapons scattered around the palace.

Princess Diana and Prince Charles looking stern at each other

Behind closed doors, the Prince and Princess of Wales' volatile marriage raised eyebrows, author Christopher Andersen alleged. (Tim Graham Photo Library via Getty Images)

"He has a huge temper," Andersen claimed about the king. "I mean, it’s an incredible temper. The tantrums constantly and throwing a bootjack [at her]. It’s a heavy wooden device for putting on hunting boots, and it’s made of iron and wood. He threw it at Diana’s head and just missed her."

It was Charles’s former valet Ken Stronach who alleged to Andersen that he was in the room "when Charles, in the middle of an argument with Diana, grabbed a heavy wooden bootjack and threw it at her, missing the princess’s head by inches," as quoted in the book.

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"But there are guns all over that palace," Anderson alleged. "They love shooting parties. So there are shotguns and handguns for security and rifles [for] security forces… they were worried that there was such violence. So many screaming and shouting [and] slammed doors. Don’t forget Diana, when she was three months pregnant with [Prince] William, she threw herself down the stairs and landed at the feet of the queen and Princess Margaret. So there [were] many violent episodes. It could have gotten much worse. And [security] was afraid that not only somebody might commit suicide, that somebody might do harm, [but] we might be talking murder. So they tried to keep the weapons away from the royals."

Prince Charles and Princess Diana wedding

King Charles and Princess Diana's marriage proved to be far from a fairy tale. According to multiple sources, it was doomed from the start. (Terry Fincher/Princess Diana Archive/Getty Images)

Andersen wrote that during the marriage, Charles "had sunk into a deep depression" and thought he "was on the verge of a nervous breakdown." He turned to one of his confidants, Arnold Goodman, and allegedly said, "I have nothing to live for." Goodman allegedly felt that Charles was "showing the classic signs of depression." Charles not only believed he was trapped in a loveless marriage, but he feared that a divorce, if it could even be granted by the queen, "would have grave repercussions for his children, the royal family and the monarchy itself."

Princess Diana looking annoyed at Prince Charles

Royal protection officers were allegedly concerned about the number of weapons around as Prince Charles and Princess Diana's marriage became so explosive. (Tim Graham Photo Library via Getty Images)

According to Andersen, Goodman expressed his concerns to royal protection officers. Ken Wharfe, Diana’s former protection officer, described the atmosphere as "highly combustible." One bodyguard told Andersen that the clashes between Charles and Diana were "so raw" that "violence seemed inevitable."

"Posing a special problem was the sheer firepower contained within Highgrove’s walls," Andersen wrote. "Guns were scattered about the premises – ‘shotguns, rifles, pistols, the whole lot’ – and the detectives in charge of protecting members of the royal family were deeply concerned that ‘in the heat of anger,’ any one of these could be used to commit suicide, homicide or both. There was also a legitimate concern that William and Harry might become collateral damage. Just to be safe, all guns were put under lock and key."

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According to housekeeper Wendy Berry, she witnessed "the slammed doors and pitched battles" that were "the hallmarks of day-to-day life." One of Charles’ valets alleged that he saw Diana chase Charles "down hallways, up staircases, and from room to room." It was then that she allegedly asked point-blank, "Why won’t you sleep with me?" Charles sarcastically replied, "I don’t know, dear, I think I might be gay."

Prince Charles looking annoyed at Princess Diana

Christopher Andersen alleged that King Charles sarcastically told Princess Diana he "might be gay" during one of their many arguments. (Tim Graham Photo Library via Getty Images)

"He was having an affair with Camilla [Parker Bowles]," Andersen explained. "He was not interested in [Diana] anymore. He shut down emotionally toward Diana. I think Diana’s gotten a very bum rap in that, since her death, no one’s really been there to defend her against these charges."

"She became neurotic, developed an eating disorder and all of these things because of the behavior of Charles and Camilla," Andersen alleged. "If indeed Camilla hadn’t been in the picture, none of that would’ve happened."

The trouble between Diana and Charles started long before their so-called fairy-tale wedding. Charles, the heir to the British throne, was allegedly pressed to either end his relationship with then-Lady Diana Spencer or propose. Before the wedding, Diana expressed doubts about walking down the aisle, especially after she discovered a bracelet Charles made for Camilla, his former flame. The marriage became tumultuous, and the unhappy couple had extramarital affairs.

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King Charles and Princess Diana looking glum

In 1992, King Charles and Princess Diana went on an official trip to South Korea together. The couple looked so miserable that they were nicknamed "The Glums" by the British press. (Tim Graham Photo Library via Getty Images)

In 1992, Andrew Morton wrote "Diana: Her True Story," a shocking tell-all about the collapsing marriage. It also detailed Charles’ relationship with Camilla, as well as Diana’s mental health struggles. At the time, it wasn’t confirmed that the princess secretly collaborated with the British author on the book. That same year, it was announced that the couple was separating. 

The divorce was finalized in 1996. A year later, Diana was killed from injuries she sustained in a Paris car crash at age 36.

Andersen said Charles was devastated by Diana’s passing. When he received the dreaded call, he allegedly clutched the telephone "ashen and trembling." He then let out "a cry of pain was that so spontaneous and came from the heart." One witness described it as a "howl of anguish" that was heard down the hall. Palace staff rushed over to Charles’ room and found him "collapsed in an armchair, weeping uncontrollably."

"Charles is responsible not only for having brought the monarchy to its knees at one point after Diana died, but also rescuing it," Andersen explained. "I don’t think people realize how really stricken he was by her death. I interviewed the nurses in the hospital who saw him when he came into the room and saw her body for the first time. And he looked like he’d been hit in the face. He reeled back. They thought he was going to faint. They were surprised to see how emotional Charles was after her death."

King Charles looking somber during Princess Diana's funeral

King Charles' grief over the sudden passing of Princess Diana left palace aides stunned, Christopher Andersen wrote. (John Giles - PA Images/PA Images via Getty Images)

Andersen said the grief-stricken Charles was determined to make sure the mother of his two sons would be honored.

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"He snapped into action and made sure the queen gave Diana the proper sendoff," he said.

Andersen noted that it was Charles who convinced his mother to give "the speech of her life" as thousands of mourners gathered outside Buckingham Palace. Following Diana’s death, many criticized the royals and insisted the monarchy was doomed.

The queen passed away on Sept. 8 at age 96. Now, Charles faces the task of preserving a 1,000-year-old monarchy. He alienated so many people with his messy divorce from the much-loved "People’s Princess," but now, all eyes are on him.

King Charles visiting a service station

Prince Charles became king of England when his mother, Queen Elizabeth II, passed away on Sept. 8 at age 96. She was Britain's longest-reigning monarch. (Chris Jackson - WPA Pool /Getty Images)

"He’s had a lot to do with the trajectory of the monarchy already," said Andersen. "If [the monarchy] is a success, it’ll be because of him. And if the monarchy goes down the drain, it’ll be because of him. We’ll have to wait and see."

A spokesperson for Buckingham Palace didn’t immediately respond to Fox News Digital’s request for comment. However, a spokesperson previously told Fox News Digital "we don’t comment on such books."

The Associated Press contributed to this report.