Prince Harry put on a brave face for King Charles and Queen Camilla's coronation – but it was far from a happily ever after for the House of Windsor.

The Duke of Sussex arrived at Westminster Abbey on Saturday for the historical ceremony alone and he left alone. The 38-year-old was assigned to sit several rows behind his brother, Prince William.

Many royal watchers were hoping the coronation would break the ice between the battling brothers. According to reports, the siblings, who were once so close, have been estranged since Harry made his royal exit in 2020. During the coronation, William and Harry were never seen speaking or even acknowledging each other. And afterward, Harry swiftly flew back to California where he lives with his wife, Meghan Markle, and their two children, Prince Archie and Princess Lilibet.

Prince Harry standing in his morning suit

Prince Harry, Duke of Sussex, is seen standing alone before the coronation ceremony of King Charles III and his wife, Queen Camilla, at Westminster Abbey. (Andy Stenning/WPA Pool/Getty Images)

"As Harry watched his father being crowned and his brother pledging his allegiance to the new king with a kiss on the cheek, he must have felt the slightest tinge of regret," Christopher Andersen, author of "The King," told Fox News Digital. "Frankly, to keep his sanity, he has to keep telling himself he made the right decision by bailing on the royal family."

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King Charles coronation

Britain's King Charles and Queen Camilla wave on the Buckingham Palace balcony following their coronation ceremony in London. (Reuters/Matthew Childs)

"Harry appeared to have no interaction with King Charles, Queen Camilla or William and [his wife] Kate [Middleton]," Andersen shared. "For his part, William seemed not at all interested in acknowledging his brother and vice versa – that is how broken this relationship is. The U.K. still holds a great deal of affection for Harry, and I'm sure the people would love to see him back in the royal fold. It just seems sad that at a time when his countrymen and women are celebrating his father's coronation, Harry could not wait to hop on a plane and get back to Montecito."

"There were no signs of reconciliation – everyone seems to have dug in," Andersen added.

A close-up of Kate Middleton and Prince William in their royal regalia

Prince William, Prince of Wales, and Catherine, Princess of Wales, on the balcony of Buckingham Palace during the coronation of King Charles III and Queen Camilla on May 6, 2023, in London. (UK Press Pool/UK Press via Getty Images)

Since the Duke and Duchess of Sussex announced they were stepping back as senior royals, they’ve repeatedly aired their grievances. Most recently, Harry wrote an explosive memoir, "Spare," which detailed his struggles with royal life, the devastating loss of his mother, Princess Diana, as well as his rivalry with William, 40, who is heir to the throne.

In the book, Harry alleged that during an argument in 2019, William called Markle "difficult" and "rude" and then grabbed him by the collar and knocked him down. Harry suffered cuts and bruises from landing on a dog bowl. Harry claimed Charles implored the brothers to make up. Following the funeral of Charles’ father, Prince Philip, in 2021, the king pleaded, "Please, boys, don’t make my final years a misery."

Neither Buckingham Palace, which represents the king, 74, nor William’s Kensington Palace office, commented on any of the allegations.

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Prince Harry in his morning suit making a funny face

Several royal watchers said Prince Harry appeared awkward as he sat several rows behind his elder brother, Prince William. (Richard Pohle/WPA Pool/Getty Images)

British broadcaster and royal expert Ian Pelham Turner told Fox News Digital that the tension between the brothers was apparent during the ceremony.

"Great Britain cannot afford to have a royal family which is fragmented and not representing the true values of the people," Turner explained. "… In my opinion, it is not [William and Harry’s] right to behave in such a dishonorable way."

"It is said by many experts that King Charles is too weak to deal with the situation, that this cannot be resolved," Turner said. "It will be resolved if the people of Great Britain turn their backs on the new king and show the [same] disdain … currently being played out in the public arena by the two brothers."

King Charles III during his coronation ceremony at Westminster Abbey, London

King Charles III is shown during his coronation ceremony at Westminster Abbey in London. (Victoria Jones/Pool via Reuters)

"In my opinion, William and Harry are playing with fire, which could erupt the whole house of Windsor in flames," he added.

Author and royal expert Katie Nicholl previously revealed in her book, "The New Royals," that even the late Queen Elizabeth II was allegedly "deeply hurt by Harry’s decision to leave his family and the country." Charles became king upon his mother’s death in September 2022 at age 96.

"According to a friend, privately the queen confided that she was exhausted by the turmoil of their decision," Nicholl wrote. "She was very hurt and told me, ‘I don’t know, I don’t care, and I don’t want to think about it anymore,' says that person."

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Queen Elizabeth with William and Harry

During happier times, Queen Elizabeth II is seen laughing alongside her grandsons, Prince Harry, left, and Prince William, at Buckingham Palace. Britain's longest-reigning monarch died in September 2022. She was 96. (Tim Graham Photo Library via Getty Images)

"It was a source of sadness to the queen that she got to see so little of Archie and Lilibet and that Harry and Meghan were not able to join her for a weekend at Balmoral in August [2022] when the queen used to host a ‘sleepover’ for all of her grandchildren and great-grandchildren," Nicholl said.

Another point of contention for the queen was the icy relationship between Charles and Harry, which allegedly "caused the queen so much upset." Nicholl also reported that the king "desperately wants to reconcile with his son."

Harry and his wife left royal life and moved to California following the intense scrutiny and racist attitudes from the British press. Markle, 41, is biracial.

A cardboard cutout of Meghan Markle outside during a coronation lunch

A cardboard cutout of Meghan, Duchess of Sussex, stands at the head of the table at a street party on Denman Road to mark the coronation of King Charles III and Queen Camilla on May 7, 2023, in London. (Rob Pinney/Getty Images)

In a six-part Netflix series, they lobbed other criticisms at the royal family, alleging racial bias.

Then in his memoir, Harry revealed private conversations he had with his father and brother. The book was particularly unflattering toward his stepmother, Camilla, who was once blamed for wrecking his father’s marriage to his mother. He accused Camilla, 75, of making leaks to the media to rehabilitate her own image after marrying Charles.

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Camilla wearing a white goiwn with a crown

On Saturday, the royal family's official website officially acknowledged Camilla as queen. (Jeff J. Mitchell/Getty Images)

Buckingham Palace had announced before the coronation that Harry and the king’s brother, Prince Andrew, would not have any role in the service. Markle stayed behind in California.

"Meghan's decision to not attend with Archie and Lilibet may have seemed like the right one at the time, given the fact that so much attention would be on her and that would have risked her being booed," said Andersen. "But Harry and Archie are now fifth and sixth in line to the throne, and the fact that she could not put aside her grievances for this once-in-a-lifetime historic event – the most important moment in her father-in-law's life – comes across to most Britons as petty and vindictive."

Prince Harry looking in the direction of his older brother Prince William during King Charles coronation

Prince Harry appeared to look in the direction of his brother, Prince William, during their father's coronation ceremony on Saturday. (Victoria Jones/WPA Pool/Getty Images)

Harry was seen entering the church in a black custom Dior three-piece suit with coattails. An honorary cross hung around his neck and military medals were pinned to the left side of his chest. He nodded, waved and spoke a few words to clergy and several guests already seated.

Meanwhile, William played a prominent role during the coronation. He kneeled at his father’s feet, pledging his loyalty and then kissing him on the cheek. His eldest son, Prince George, served as a page boy, helping to carry the train of his grandfather’s robes.

During the two-hour spectacle, keen attention was focused on Harry by the media and royal watchers. Next to him was his cousin, Princess Eugenie, and her husband, Jack Brooksbank.

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Prince Harry in his morning suit chatting with Jack Brooksbank

Prince Harry has a close bond with his cousins, Princess Eugenie and Princess Beatrice, as well as their husbands. (Aaron Chown/WPA Pool/Getty Images)

Andersen noted that Harry’s cousins are his "closest friends and allies among the royals."

"Harry looked profoundly awkward and decidedly out of place like a spare part at the coronation," British royals expert Hilary Fordwich told Fox News Digital. "… While he has a decidedly dubious future at best, his brother, William’s, future is more solid and secure than ever."

Prince William in royal regalia touching his father King Charles crown during the coronation ceremony

Prince William is heir to the British throne. (Yui Mok/WPA Pool/Getty Images)

"In contrast to Harry’s slightly strange entrance, there were profoundly touching moments between the king and the Prince of Wales," she said. "There were solid father-and-son moments between them, demonstrating deep rapport. One wonders if the deep appreciation that the king had for William by mouthing ‘Thank you’ was for much more than the components of the service and his paying homage."

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A close-up of Prince William kissing his father King Charles

Prince William, Prince of Wales, kisses his father, King Charles III, during the coronation ceremony. The king was seen whispering a heartfelt "thank you" to his son. (Yuki Mok/Getty Images)

Royal expert Kelly Lynch told Fox News Digital that the ceremony would have made it difficult for the brothers to have any kind of heartfelt talks. However, she suspected that this could very well be "Harry’s final appearance with his family."

"At this point, both sides should put down their swords and move on with their lives – Harry and Meghan to whatever good works they've set out to do and the royal family to continue upholding tradition and history as so many houses before them have," she said. "It's sad to watch. No family wants to fight, especially siblings."

The final glimpse of Harry was that of him quickly arriving at Heathrow Airport. His son turned 4 on Saturday, and it was said he headed back for his birthday.

Prince Harry in his morning suit entering a black car

Prince Harry is shown leaving Westminster Abbey after the coronation of King Charles III and Queen Camilla on May 6, 2023, in London. (Getty Images)

A short while later, the king and his queen stepped out onto the balcony of Buckingham Palace. They were joined by William and his family.

The Associated Press contributed to this report.