It was one of the biggest scandals of the 1960s — and maybe one of the first public examples of revenge porn.

When “A Very British Scandal” premieres Friday on Amazon Prime, it will be the first time that most Americans learn all about Margaret, the Duchess of Argyll; her husband Ian Campbell, the Duke of Argyll — and the ill-fated string of pearls that proved to be her downfall during their bitter and lascivious divorce battle.

The duchess was the Kim Kardashian of her day, a socialite photographed every time she stepped out on the town and famed for a string of affairs.

But it all came crashing down when Campbell used photos he had stolen of his wife “in flagrante” with another man to shame her in court during their 1962 divorce. It worked, with Judge Lord Wheatley blasting her as “a completely promiscuous woman” whose attitude towards marriage was “wholly immoral.”

The judge, a highly conservative Jesuit and a relative of Campbell, added: “I consider her to be a highly sexed woman who had ceased to be satisfied with normal relations and had started to indulge in disgusting sexual activities to gratify a debase sexual appetite.”

As The New York Times reported at the time, the photos “reportedly showed a naked man gratifying himself and pictured [the duchess], dressed in nothing but three strands of pearls, performing a sex act on a naked man in the mirrored gilt and silver bathroom of her Mayfair apartment.”

“Margaret really invented the tabloid scandal, which now is such a huge industry,” show writer Sarah Phelps told The Post. “I thought of all those terms like ‘slut shaming’ while writing, although that’s been around forever and a day!”

Phelps said the duchess was like Kim Kardashian “In terms of how much she was looked at … and she loved that, when it was good.  

“She’d been engineered, she’d been groomed and guided and educated to be be the cynosure of all eyes, to be somebody who was beheld: the best dressed, the most beautiful and the most notorious. So the idea of not being looked at was anathema — until it came to the point where being looked at was punishment for being visible.”

Although the duchess was identified by her trademark pearls, her lover remains officially unidentified to this day and is usually referred to as “the headless man.”

In 2000, a BBC documentary purported there were actually two photos showing men whose faces weren’t visible. According to sources in “Secret History: The Duchess and the Headless Man,” one was former Minister of Defense (and son-in-law of Winston Churchill) Duncan Sandys — based on the duchess’s statement that “the only Polaroid camera in the country at that time had been lent to the Ministry of Defense,” as well as the memory of one of her confidants. The other, the documentary claimed, was Hollywood actor Douglas Fairbanks Jr.

The duchess took her secrets to her death.

Claire Foy, who played a young Queen Elizabeth II in “The Crown,” stars as the duchess in the show, while Paul Bettany has the role of Campbell.

“There is something delicious about watching people tear each other to shreds — especially when they’re played by Claire Foy and Paul Bettany,” said Phelps.

Margaret Whigham was born in Scotland to industrialist George Hay Whigham and his wife, Helen Mann Hannay. She spent the first 14 years of her life in New York City, before returning to London as a teenager in the 1920s.

Her mother was so strict that Margaret was sent to have a perm and get her eyebrows plucked aged 9 to “improve her looks,” Phelps said, and was forced to have her left arm tied behind her back to train her to write with her right hand. When this prompted a nervous stutter, her mother got her tutor to tie her right hand back, but it only made her stutter worse.

The future duchess was named debutante of the year in 1930 and had high-profile romances, getting engaged to Prince Ali Kahn before marrying wealthy American Charles Sweeney in 1933.

The couple, who had three children, divorced in 1947; four years later she wed Campbell, who had a family castle, Inveraray, in Scotland.

The marriage was soon in trouble: The duke was cruel and known to be addicted to drink, gambling and prescription drugs. Suspicious that his wife had been unfaithful, Campbell hired a locksmith to break into his wife’s private drawers while she was away in New York.
Inside, he discovered a cache of evidence of her infidelities, including the Polaroids.

In addition to submitting the photos in court, he included a list of 88 men he accused his wife of having sex with — a roster that reportedly counted cabinet members, Hollywood actors and members of the royal family among its ranks.

Many of the men on the list were actually gay men. Had Margaret acknowledged that in court, they would have gone to prison at a time when homosexuality was still a criminal offense under British law.

The case became a tabloid scandal, with headlines decrying “the dirty duchess.”

In 1993, then British Prime Minister John Major sealed the report from an investigation into the matter for 70 years, for reasons unknown. It remains in the National Archive at Kew, South West London, and isn’t schedule to be released until 2063.

There was also speculation the lover was William “Bill” Lyons, then the sales director of Pan Am, according to the duchess’s daughter-in-law lady Colin Campbell, who told Tatler: “He’s the one that Margaret told me was in the Polaroid.”

Phelps doubts that it is Lyons, however: “Nobody gives a s–t about an executive from Pan Am!”

The writer added: “In choosing to go to court, Margaret set fire to all of those preconceptions about the way the upper class and the rich behaved — she pulled the pants down of the aristocracy and she it to the ground. Then there comes a revolution, with the Beatles, the Rolling Stones, Vietnam, Twiggy and the Profumo Affair, and she was standing on the crest of that wave.”

Phelps said she was most shocked by the venom both the duchess and Campbell put into fighting each other, including bugging phones and bribing people: “It was the sheer extent of the smashes across the net that surprised me.

“‘How much more can you do to each other?’ ‘Oh no, here comes another one.’”

But she was stunned to find out that Campbell and his doctor had conspired to put the duchess in a lunatic asylum — a bid which was foiled by Margaret’s own doctor.

Just weeks after the divorce was finalized, with Margaret broke and ruined, Campbell married a wealthy American, Mathilda Coster Mortimer Heller.

In 1990, three years before her death aged 80, the duchess reminisced about her life to the Telegraph, saying: “I do not forget. Neither the good years, in which I laughed and danced and lived upon a cloud of happiness; nor the bad years of near despair, when I learned what life and people and friendship really were.”