On June 3, 1937, the Duke of Windsor, Prince Edward married American divorcee Wallis Warfield Simpson, for whom he had abdicated the British throne. It was called the "romance of the century." (National Archives)

It has been formally announced this 27th day of November in the year 2017 that a British royal — Prince Henry of Wales (known to drinking buddies as Prince Harry) — is marrying an American divorcée.

The last time this happened — in 1936 when King Edward VIII decided to wed American socialite Wallis Simpson — it triggered a crisis inside Windsor Castle.

For one thing, Simpson was about to divorce for the second time. Also, she was from Baltimore.

The king faced a choice: Dump “that woman,” as Simpson became known, or dump the throne.

He dumped the throne.

The extraordinary moment in the history of the monarchy has been recounted in countless books, movies and TV shows — most recently in the hit Netflix series “The Crown,” which dramatizes Queen Elizabeth’s rise to the throne.

It goes roughly like this: King Edward falls into forbidden love. King Edward abdicates. His brother George takes the throne. George dies. Elizabeth becomes queen. The end.

What the show, and history, often leave out was how this succession of events — which forever altered succession to the throne — was set in motion by a truly strange and unlikely love affair.

Simpson was born in Pennsylvania as Bessie Wallis Warfield. Her father was a wealthy flour merchant who died of tuberculosis a few months after she was born. Wallis and her mother moved to a Baltimore rowhouse, living on meager monthly payments from her late father’s brother.

It was “cheese-paring poverty,” historian Philip Ziegler wrote, and Simpson was “resentfully aware that her friends could afford nicer clothes and more lavish holidays.”

Wallis decamped for Florida after her uncle declined to host her coming-out ball, according to Anne Sebba’s 2012 biography, “That Woman.” There, in the early 1900s, she met husband No. 1: Win Spencer, a Navy pilot. They divorced a decade later. He drank a lot. They fought a lot.

Next up: Ernest Simpson, a Harvard grad who renounced his U.S. citizenship and worked with his father in the British shipping industry, giving Wallis access to high-society London. Simpson’s New York Times obituary noted that he “ruefully” referred to himself as “the Forgotten Man,” the result of being dumped for a king.

Actually, Edward was just a prince when he first met Wallis at a party in 1931, a year that represented a busy period in which the prince had two other girlfriends. But they didn’t have what Wallis possessed: an American accent.

“Those who spoke with an American accent had a much easier chance of amusing the Prince,” Sebba wrote. “He liked almost everything that characterized as new and modern and much of it was American.”

It was not love at first sight, though.

Their courtship took place over a series of years and parties. Wallis became one of the prince’s three main squeezes. Then, in 1934, the prince settled on Wallis as his favorite —  or “favourite,” as the British biographers spell it — dumping the other two.

In deference to the royal family, the British press largely avoided much mention of their relationship, even after George became king when his father died in early 1936.

Wallis was still married to Simpson.

And then, on Oct. 15, 1936, the following headline appeared above an Associated Press story in The Washington Post, setting off chaos in the monarchy:

“Freedom” meant divorce.

“The actual divorce action,” the AP story said, “under ordinary circumstances, is a mere formality, consisting of only a few minutes testimony.” These circumstances were not ordinary, for the cause of the divorce — adultery — was committed by the king.

Negotiations over the divorce, however, resulted in an agreement between the parties that “under no circumstances,” the AP reported, “will the name of King Edward be mentioned in court, nor will any reference be made to him.”

Their relationship could not be left officially unsaid forever, especially because King Edward wanted to marry the Baltimorean. The king, however, could not reasonably do so. For one thing, he was the head of the Church of England, which did not allow remarriages. And the government would have collapsed over the matter.

So he abdicated, telling the world in a radio broadcast that:

A few hours ago I discharged my last duty as king and emperor, and now that I have been succeeded by my brother, the Duke of York, my first words must be to declare my allegiance to him. This I do with all my heart.

You all know the reasons which have impelled me to renounce the throne. But I want you to understand that in making up my mind, I did not forget the country or the empire, which, as Prince of Wales and lately as king, I have for 25 years tried to serve.

But you must believe me when I tell you that I have found it impossible to carry the heavy burden of responsibility and to discharge my duties as king as I would wish to do without the help and support of the woman I love.

And I want you to know that the decision I have made has been mine and mine alone. This was a thing I had to judge entirely for myself. The other person most nearly concerned has tried up to the last to persuade me to take a different course. I have made this, the most serious decision of my life, only upon the single thought of what would, in the end, be best for all.

Edward ended his address, “God save the king!”

Only now, the king was a duke.

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