King Charles III was crowned Saturday in a once-in-a-generation coronation spectacle at London’s Westminster Abbey — but the historic occasion was marred by family drama.

In a dazzling display of royal triumph, Charles, 74, sat upon the 700-year-old oak Coronation Chair in front of world leaders, foreign royals and celebrities for Britain’s biggest ceremonial event in seven decades.

For the first time since the late Queen Elizabeth II’s coronation in 1953, Britain crowned a new monarch.

“I come not to be served but to serve,” Charles declared.

However, amid the excitement and pomp and ceremony, the service marked the first time that rogue royal Prince Harry, 38, came face-to-face with his dad since the release of his protocol-shattering memoir, “Spare.”

It’s also the first time Harry saw his estranged brother and heir to the throne Prince William, 40, his wife, Kate Middleton, 41, and their kids — Prince Louis, 5, Princess Charlotte, 8, and Prince George, 9.

Meanwhile, scandal-scarred Prince Andrew, 63, who has been tied to pedophile Jeffrey Epstein, was loudly booed as he traveled through London to attend the ceremony.

As non-working royals, Harry and Andrew were notably shunned from any official role in the coronation service — and neither took part in the joyous procession back to the palace or appeared on the Buckingham Palace balcony.

The royal outcasts were also relegated to third-row seats during the service, two rows behind the Prince of Wales and his family.

Harry, dressed in his morning suit spiffed up with a line of medals, walked up the aisle to his seat alone, as wife Meghan Markle, 41, remained thousands of miles away in California with their kids, Archie — who turned 4 Saturday — and Lilibet Diana, 1.

Once seated, he nodded at other guests as he joked with Jack Brooksbank, the husband of his cousin Princess Eugenie.

At one point, the flame-haired prince seemed to be aware of the tension overshadowing the momentous occasion and pulled an exaggerated, uneasy smile.

“I bet he can’t wait to leave,” one royal watcher noted on social media.

Andrew, meanwhile, was permitted to wear traditional garter robes, which raised some eyebrows.

Earlier reporting suggested that, as a non-working royal and spectator in the ceremony, he would be reduced to wearing a morning suit like his estranged nephew.

Outside the Abbey, spectators criticized the new king’s willingness to include his straying son in his momentous day.

“Harry should not be here. He’s been very disloyal to the royal family,” Jaquie Cullen, of Liverpool, told The Post.

“I was a big fan of Harry before Meghan came around. He was a good, cheeky kid,” Cullen’s husband, Bernie, added.

Mal Hill, 63, of Manchester also said she was “not too happy about Harry attending.”

“I think he’s not stuck to the code,” she scoffed. “If he had something to say he should’ve said it to the family.”

The King’s disgraced brother Andrew was also met with a chorus of boos as he drove past royal fans camped out on the Mall in a state car on the way to the ceremony.

Still, some royalists were more forgiving of the presence of the Duke of York, who was infamously stripped of his royal and military honors amid his sex abuse lawsuit with Jeffrey Epstein accuser Virginia Roberts Giuffre in Jan. 2022. The case was settled in February 2022 and Andrew admitted no wrongdoing.

“Harry scarred the British spirit more than Andrew,” Jaquie Cullen argued. “Because against Andrew are only allegations but Harry has done the unforgivable.”

Bernie Cullen added: “You just don’t air out your dirty laundry in public at all.”

In the day’s most pivotal moment, the new monarch, robed in golden priest-like garb, took his seat in a 700-year-old piece of furniture: the magnificent Coronation Chair.

The throne was built in 1300 for Edward I when he added Scotland to his realm.

It encloses the legendary Stone of Scone – dramatically dubbed the Stone of Destiny by some – and has been used at many coronations since the 14th century.

Charles sat stoically as he received a succession of symbolic objects: swords, scepters, and the Sovereign’s Orb, all fabulously bejeweled and representing his mercy, justice and power.

Finally, Justin Welby, Archbishop of Canterbury, placed the heavy, centuries-old St. Edward’s Crown on Charles’s head to signify his coronation.

The monarch appeared to buckle slightly under the crown’s nearly five pounds of gems and solid gold, but he quickly straightened as he stared ahead with moist, emotional eyes.

Moments later, Prince William knelt before his father as heir to the throne and swore his loyalty, pledging to serve as Charles’s “liege man of life and limb” – the same promise made by his grandfather Prince Philip to Elizabeth II, his wife, during her coronation in 1953.

The Prince of Wales gently touched the crown that he may one day wear himself, then bent to kiss his dad’s cheek.

To complete the family circle, Camilla was anointed with holy oil and Queen Mary’s Crown was placed on her head – as she flashed a grin to the crowd and gave a whisper of a wink to her husband.

The coronation festivities began at 10:20 am local time as a military band played “God Save the King” for Charles and Camilla as they left Buckingham Palace in the Diamond Jubilee State Coach.

Moments earlier, the Royal Family’s website ditched the “Queen Consort” title that it had previously used for Camilla – referring to her for the first time as “The Queen.”

“Her Majesty The Queen (formerly HRH The Duchess of Cornwall) supports her husband, formerly The Prince of Wales, now His Majesty The King, in carrying out his work and duties,” the website now reads.

Thousands of spectators lined the streets of London, braving the rainy weather, and cheered for their new king.

“It’s amazing seeing Brits all come together like this. It’s what we do best. Pints and pride,” Thomas Burns, 66, told The Post.

Charles formally took the throne eight months after the 70-year reign of his mother Queen Elizabeth II ended with her death in September.

He is the 40th monarch to be crowned in Westminster Abbey since it was established in the 11th century as the home of the nation’s most solemn ceremonies.

Prince George, 9, now second in line to the throne, served his grandfather as a page, garbed in a long red jacket and gloves.

He followed Charles into the church as a choir sang a greeting – and afterward, along with three other young boys, hoisted the king’s long purple robe over puddles as he entered the Gold State Coach for the 1.3-mile ride back to Buckingham Palace.

More than 4,000 military members joined the new king in a grand parade as a chilly rain soaked the capital.

Charles, now wearing the priceless Imperial State Crown, and Camilla were seen chatting throughout the journey, occasionally breaking off their conversation to wave to the crowds.

Princess Anne, Charles’s sister, followed their elaborate 18th-century carriage on horseback as she led the troops in her ceremonial role as Gold Stick in Waiting, the king’s personal bodyguard.

Immediately behind her rolled the Diamond Jubilee State Coach now containing William, Kate, and their children.

Little Prince Louis pulled a series of adorable faces as he peered out of the carriage’s windows, while Princess Charlotte waved energetically at the throngs.

But amid the sea of Union Jacks, anti-monarchy demonstrators dotted the route, booing as the new king and queen passed.

“Down with the crown!” and “Not my King!” shouted protesters who waved blinding yellow signs as their carriage rolled along.

Six demonstrators with Republic, a group aimed at abolishing the monarchy, were detained and searched early Saturday, the organization’s director Harry Stratton told CNN.

Meanwhile, Prince Harry hastily left London less than an hour after his father was crowned, rushing home to California to join his son’s birthday celebration.

Harry was in the UK for less than 24 hours after arriving via commercial flight Friday evening.

As the runaway son headed to Heathrow Airport, two dozen members of the royal family gathered on the balcony of Buckingham Palace to greet the crowds and marvel at a two-minute military flyover featuring five waves of helicopters and a formation of Royal Air Force Red Arrows trailing the blue, white, and red colors of the national flag.

With additional reporting by Nika Shakhnazarova and Olivia Land