Jeanne de Saint-Remy, Comtesse de la Motte, was a highly placed confidence woman whose greatest scam, the "Affair of the Diamond Necklace," sped the fall of the French monarchy. In spite of her self-serving and vengeful memoirs, published in England, most historians believe that she was guilty of the crimes of which she was convicted.
The French jewelry firm Boehmer and Bassenge had invested a great deal of money into the stones needed to make a great necklace of diamonds, which they attempted unsuccessfully to sell, first to Madame du Barry, the mistress of Louis XV, and then to Louis XVI's wife, Marie Antoinette. This necklace became an incredibly expensive prop in a convoluted intrigue: Louis René Édouard, Cardinal de Rohan, was out of favor with the queen, and wished to regain her good graces. The Comtesse de la Motte claimed to him that she was a favorite of the queen and could effect reconciliation. She then encouraged the cardinal to correspond with the queen, but she herself provided the answers, which were inscribed by a confederate and signed with the queen's name. She even arranged a meeting with a Marie Antoinette impersonator, and after a while the cardinal became persuaded that not only was the queen no longer angry with him, she was in love with him. The comtesse then convinced him that the queen wanted to buy the great diamond necklace – and that he should negotiate the purchase for 1,600,000 louis d'or, which he did, apparently in good faith. He then handed the necklace over to the comtesse for delivery. The deception came to light when the jewelers asked to be paid.
The necklace was never seen again, and probably was taken to England and broken up. The cardinal, the comtesse, her friend who had forged the letters, and a handful of others were arrested. The case convulsed both public and the court. The queen was unpopular and the French public mostly believed that she had actually ordered the necklace as part of a plot to destroy the cardinal. The forged correspondence was assumed to be hers and to be evidence of her sexual misdeeds. The trial, which was as much about the queen as the theft of the necklace, ended with Marie Antoinette's reputation damaged; the cardinal was acquitted, the comtesse and the forger convicted. The comtesse escaped to London and published her Memoirs, blaming Marie Antoinette for the whole affair; she died only five years later.