It is a story whose characters and actions are so implausible that at times it seems like the wild invention of a work of fiction. But the Diamond Necklace Affair was a scandal that was all too responsible for the eventual execution of Marie Antoinette—the last Queen of France before the French Revolution.

Most shocking, perhaps, is that the Queen was totally unaware of the elaborate scam.

It all began with a dubious “countess”—Jeanne de Valois-Saint-Rémy—the self-styled “Comtesse de la Motte,” who passed herself off as a descendant of the former French royal family, the Valois, but whose links to nobility were fairly dubious. Realizing that her husband’s paltry income would never fund the extravagant lifestyle she desired, La Motte thought she could win the favor of the queen herself, who, hearing of La Motte’s shady background, refused to meet her.

Undaunted, La Motte took a lover, Rétaux de Villette, a soldier who served with her husband, and also, in 1783, became the mistress of the prestigious Cardinal de Rohan. The cardinal, who had been French ambassador to Vienna a few years earlier, had fallen foul of Marie Antoinette’s mother, the Empress Maria Theresa, and wanted nothing more than to win back royal approval. La Motte saw her chance.

She discovered that the jewelers Charles Auguste Boehmer and Paul Bassange were trying to sell off an extraordinarily expensive necklace that had originally been designed for Madame du Barry, the mistress of the former king Louis XV. The necklace was worth an estimated 2,000,000 livres (roughly $15 million today). At the death of the King, the necklace was unpaid for, and the jewelers were facing bankruptcy. They had already tried to sell it to the current king, Louis XVI, but the Queen refused, saying “We have more need of Seventy-Fours [ships] than of necklaces.”

La Motte, an inveterate con-artist, persuaded the cardinal that she enjoyed the Queen’s secret favor. On hearing of this, Rohan resolved to use her to regain the Queen's goodwill. La Motte encouraged the cardinal to begin writing to the Queen, and claimed to pass on the letters to her. In reality, and along with her other lover Villette, a forger, she created her own replies from “the Queen.” In these fake letters, the Queen spoke of her desire for the necklace, but, aware of the reluctance of the King to buy it due to the current dire financial situation of the country, she hoped that the cardinal could lend her the money as a secret favor.

The cardinal believed these letters to be authentic and agreed to buy the necklace for the Queen. A late-night secret liaison was arranged in the garden of the Palace of Versailles, where the cardinal was to meet “the Queen.” In reality, La Motte sent a prostitute who resembled the Queen, called Nicole le Guay d'Oliva), who assured him of her forgiveness. Now completely convinced of his close relationship with the Queen, the cardinal contacted the jewelers, agreeing to pay for the necklace in installments.

The jewelers were told to give the necklace to La Motte, who passed it on to her husband, who immediately began selling off the individual diamonds in London. The swindle was finally uncovered when the cardinal did not make his first installment and was unable to produce the necklace. The jewelers complained to the Queen—who revealed her ignorance of the entire affair.

The cardinal was arrested, along with La Motte, the forger, Villette, the prostitute, d’Oliva and Count Cagliostro, one of the cardinal’s clients, whom La Motte accused of having orchestrated the entire con.

The cardinal was acquitted and exiled to one of his own properties in southern France. Rétaux de Villette was found guilty of forgery and exiled. Nicole d'Oliva was acquitted. Count Cagliostro, though acquitted, was exiled from France by order of the King.

Jeanne de la Motte, the adventuress at the heart of the story, was found guilty and sentenced to be whipped, branded and imprisoned for life in the Salpêtrière, a notorious prison for prostitutes. However, she managed to escape disguised as a boy and made her way to London where, in 1789, she published her memoirs. Unsurprisingly, she blamed Marie Antoinette for the whole affair.

Louis XVI and Marie Antoinette, although completely unaware of the scam, had decided to publicly prosecute to defend their honor. Unfortunately, this had the opposite effect, destroying the reputation of the Queen, whom many believed had manipulated La Motte to wreak revenge on her enemy, the cardinal. The affair entirely discredited the Bourbon monarchy in the eyes of the people, and the Queen’s reputation would never recover from the incident.

Only a few years later, she would face the guillotine, the dying symbol of the corruption of the ancien régime.