Prince William was concerned about Prince Harry’s relationship with Meghan Markle, and it wasn’t just because he felt they were moving at lightning speed.

The claim was made by former Vanity Fair editor Tina Brown, who recently wrote a bombshell book about the royals titled "The Palace Papers: Inside the House of Windsor – the Truth and the Turmoil." It explores "the scandals, love affairs, power plays and betrayals" that have rocked the British royals during the last 20 years and features new revelations based on Brown’s access to palace insiders.

The bestselling author previously wrote a biography on the Princess of Wales titled "The Diana Chronicles," which was published in 2007. For her latest book, Brown said she spoke to more than 120 sources who were close to senior members of the royal family.

Brown claimed that William, 39, didn’t believe the former American actress could handle the pressures of royal life.

PRINCE WILLIAM HAD A PANIC BUTTON INSTALLED IN KATE MIDDLETON’S APARTMENT WHEN THEY DATED, BOOK CLAIMS

Prince William Prince Harry Meghan Markle

Prince William was concerned that Meghan Markle couldn't handle the pressures of royal life. (Eddie Mulholland - WPA Pool/Getty Images)

"A person close to the Duke of Cambridge told me that William thought she should have more time to build up a life in the U.K. and make friends who didn’t always have to be brought in confidence to the palace," Brown wrote. "It had been hard enough for Kate [Middleton], but Meghan was a glamorous actress who would be the first woman of color to join the royal family, factors that would add enormously to the pressure."

"Unspoken to Harry, the person said, was the older brother’s fear that Harry’s mental fragility was such that he wouldn’t be strong enough to handle all of that on her behalf, as well as his own issues," Brown added.

William’s relationship with Middleton moved at a much slower pace, in comparison.

The Duke and Duchess of Cambridge met in 2001 as students at the University of St Andrews in Scotland. William told The Telegraph they were friends for over a year before a relationship blossomed. While the tabloids reported that the couple called it quits in 2007, they had reportedly gotten back together later that year.

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Tina Brown Princess Diana

Tina Brown previously wrote a book about Princess Diana. (Tim Graham Photo Library via Getty Images)

According to Brown, Middleton wasn’t entitled to official protection from the palace during their courtship.

"William reportedly arranged for a panic button to the local police station to be installed in her apartment to protect her from the constant threats of intrusion," Brown wrote.

She also shared that Middleton would sometimes receive assistance from Prince Charles’ former communications director, Paddy Harverson.

Working senior members of the royal family and their spouses are entitled to publicly-funded police protection. Middleton didn’t become entitled to police protection until she married the prince.

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Prince William Kate Middleton

Prince William's relationship with Kate Middleton moved at a much slower pace than Prince Harry's relationship with Meghan Markle. (Ben Birchall - WPA Pool/Getty Images)

William proposed to Middleton, 40, in 2010 during their vacation to Kenya. The couple tied the knot in 2011. They share three children.

Brown alleged that Harry’s response to his sibling’s concerns was to try to move faster.

"To his brother’s concerns, Harry’s riposte can be summarized as, I am told, ‘Well, actually the best way I can protect her is marry her as quickly as possible because as soon as I marry her she will then get police protection.'"

Harry, 37, and the former "Suits" star, 40, met in 2016 on a blind date. The relationship was said to have gone from "0 to 60."

PRINCE WILLIAM ‘WAS ABSOLUTELY SURE’ KATE MIDDLETON COULD HANDLE ROYAL LIFE BEFORE MARRIAGE, BOOK CLAIMS

Prince Andrew

A member of Prince Andrew's household allegedly leaked the news of Prince Harry's relationship with Meghan Markle. (Steve Parsons/Pool Photo via AP)

Just four months after the two began seeing each other, news broke of their whirlwind romance. Brown alleged that it was a member of Prince Andrew’s household, either with or without the Duke of York’s knowledge, that leaked the news.

"In the first round of coverage, [Meghan] was portrayed as Grace Kelly redux, an actress, humanitarian and gender equality campaigner, making it hard not to believe that the initial leak came from Meghan’s side (though a servant tip from the House of York had been fingered)," Brown wrote. "The second round, however, struck a different tone, forcing Meghan to experience the full-on bare-tooth barracuda swarm of hacks on the royal beat."

"American celebrities often find themselves dazed by the sheer demonic creativity of the British popular press," Brown added.

Brown claimed that a member of Andrew’s household leaked the news to the U.K.’s Sunday Express.

PRINCE WILLIAM WAS ‘APPALLED’ BY QUEEN ELIZABETH'S CHRISTMAS PHOTO SNUB OF PRINCE HARRY, MEGHAN MARKLE: BOOK

Meghan Markle

Meghan Markle became the Duchess of Sussex when she married Prince Harry. (Getty)

"Harry has been desperate to keep the relationship quiet because he doesn’t want to scare Meghan off," the source told the outlet. "He knows things will change when their romance is public knowledge, but he also knows he can’t keep it a secret for long. It’s too early to say if the relationship will lead to anything long-term but who knows? At the moment they are just taking it a step at a time and seeing how things develop."

Harry proposed in 2017.

A palace spokesperson didn’t immediately respond to Fox News Digital’s request for comment concerning Brown’s book. However, a spokesperson previously told Fox News Digital that the palace doesn’t generally comment "on such books." A spokesperson for the Duke and Duchess of Sussex also didn’t immediately reply to Fox News Digital’s request for comment.

Markle became the Duchess of Sussex when she married Harry in May 2018 at Windsor Castle. The couple welcomed a son named Archie Harrison Mountbatten-Windsor in 2019.

PRINCE WILLIAM, KATE MIDDLETON DODGE QUESTION ABOUT PRINCE HARRY WANTING TO PROTECT QUEEN ELIZABETH

Meghan Markle

The Duke and Duchess of Sussex reside in California with their two children. (Patrick van Katwijk/Getty Images)

The Duke and Duchess of Sussex’s departures from royal duties began in 2020 over what they described as the British media’s intrusions and racist attitudes toward the duchess. The family now resides in the coastal city of Montecito, California.

In the wake of quitting royal duties, they gave an explosive TV interview to Oprah Winfrey in March 2021, in which the couple described painful comments about how dark Archie’s skin might be before his birth. The duchess talked about the intense isolation she felt inside the royal family that led her to contemplate suicide.

Buckingham Palace said the allegations of racism made by the couple were "concerning" and would be addressed privately.

In June of that year, the couple welcomed their second child, a daughter named Lilibet "Lili" Diana Mountbatten-Windsor. The name pays tribute to both Harry’s grandmother, Queen Elizabeth II, whose family nickname is Lilibet, and his late mother, Princess Diana.

The Associated Press contributed to this report.