Prince William and Prince Harry once had a strong bond – but the public shouldn’t expect them to reconcile anytime soon.

The Duke of Cambridge and the Duke of Sussex will have all eyes on them on Thursday as they unveil a statue of their mother, Princess Diana, on what would have been her 60th birthday. The event in the Sunken Garden at London’s Kensington Palace will be their second public meeting since Harry, 36, and his wife Meghan Markle stepped away from royal duties over a year ago.

On Wednesday, royal historian Robert Lacey told The Associated Press the public shouldn’t expect a quick resolution between the princes because they are fighting over core beliefs. While William, 39, is defending the monarchy, Harry is defending his wife.

"It’s a matter of love versus duty, with William standing for duty and the concept of the monarchy as he sees it," the author told the outlet. "And then from Harry’s point of view, love, loyalty to his wife. He is standing by her. These are very deeply rooted differences, so it would be facile to think that there can just be a click of the fingers."

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Royal watchers will be looking closely for any signs of a truce — or deepening rift — between Prince Harry (left) and Prince William.

Royal watchers will be looking closely for any signs of a truce — or deepening rift — between Prince Harry (left) and Prince William. (Getty)

Lacey, who is also the official consultant on Netflix’s "The Crown," has updated his book "Battle of Brothers: William and Harry – The Inside Story of a Family in Tumult" with added chapters and new material. In the original book, which was published in 2020, the British historian addressed the ongoing woes impacted by the royal family.

According to the outlet, the relationship between the brothers became further strained in March when Harry and Markle, 39, gave an explosive interview to Oprah Winfrey.

During the sit-down, Harry confirmed rumors that he and his brother had been growing apart, saying "the relationship is space at the moment." He added that "time heals all things, hopefully." Harry also told the media mogul, 67, that their father, Prince Charles, didn’t accept his calls for a time.

In a revelation that even left Winfrey stunned, the couple revealed that before the birth of their first child, an unidentified member of the royal family had expressed concern about how dark his skin might be. Harry later said that the person in question wasn’t his grandmother Queen Elizabeth II or his grandfather Prince Philip.

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

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

Days after the broadcast, William responded, telling reporters, "We are very much not a racist family."

Despite their disagreements, William and Harry will put their differences aside out of respect for their mother during the statue ceremony.

"We’re not going to see any acrimony or animosity between the brothers on Thursday," historian Ed Owens told the outlet.

Owens is the author of "The Family Firm: Monarchy, Mass Media and the British Public 1932-1953," which examines the royal family’s public relations strategy.

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Days after the Oprah Winfrey interview, Prince William responded, telling reporters, "we are very much not a racist family."

Days after the Oprah Winfrey interview, Prince William responded, telling reporters, "we are very much not a racist family." (AP )

"I think reconciliation is a long way off, but nevertheless these are expert performers," Owens explained. "Harry and William have been doing this job for long enough now that they know that they’ve got to put, if you like, occasional private grievances… aside for the sake of getting on with the job."

Lacey said he believes William and Harry will ultimately reconcile because it is in both of their interests to do so. He noted Harry and Markle need to repair relations "to protect the aura of royalty" that has helped them secure contracts with Netflix and Spotify, which is helping to fund their life in California.

Lacey warned that if they don’t, they risk ending up like the Duke and Duchess of Windsor who were shunned by the royal family after the duke gave up the throne in the 1930s to marry an American divorcee. His brother, the queen's father, became king. As for the couple, they were later seen as "irrelevant."

"It’s very appealing, particularly in America, the idea that they rebelled against this stuffy old British institution," Lacey explained. "But there’s a point they can’t go too far, and they’re approaching that point. On William’s side, it is impossible to go on ostracizing, boycotting the only members of the royal family who are of mixed race in a multiracial world of diversity."

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Royal historian Robert Lacey said the Duke and Duchess of Sussex risk becoming irrelevant like the Duke and Duchess of Windsor if they don't work out their differences.

Royal historian Robert Lacey said the Duke and Duchess of Sussex risk becoming irrelevant like the Duke and Duchess of Windsor if they don't work out their differences. (Photo by Fox Photos/Getty Images)

Lacey hopes that a more public display of reconciliation will be seen next year, when their grandmother celebrates her platinum jubilee, marking 70 years on the throne. The queen normally wants her whole family together on the balcony of Buckingham Palace, where they traditionally wave to the public together.

"Who’s going to be on the balcony at Buckingham Palace?" Lacey asked. "That family grouping has surely got to include Meghan and Harry and their two children, Archie and Lili, alongside their cousins, the children of William and Kate [Middleton]."

Markle, a former American actress, 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.

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 towards the former "Suits" star. The family now resides in the coastal city of Montecito, Calif.

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Britain's Prince Harry poses with Meghan Markle in the Sunken Garden of Kensington Palace, London, Britain, November 27, 2017. REUTERS/Toby Melville - RC1DEF845A40

The Duke and Duchess of Sussex currently reside in California with their two children. (Reuters)

On June 4, the couple welcomed their second child, a daughter named Lilibet "Lili" Diana Mountbatten-Windsor. The child is eighth in line to the British throne.

The name pays tribute to both Harry’s grandmother, whose family nickname is Lilibet, as well as his late mother.

The Associated Press contributed to this report.