The Affair of the Diamond Necklace (, "affair of the Queen's necklace") was an incident from 1784 through 1785 at the court of King Louis XVI of France involving his wife, Queen Marie Antoinette. 

The reputation of the Queen had already been ruined by gossip. The event is historically significant as one of the events that led to the French populace's disillusionment with the monarchy and led to the French Revolution.

The necklace
In 1772, Louis XV of France decided to make Madame du Barry, with whom he was in love with, a special gift at the cost of 2,000,000 livres (about $15.1 million in 2020 USD). He wanted Parisian jewelers Charles Auguste Boehmer and Paul Bassange to create a diamond necklace that would be the greatest necklace ever made.

Event
A trickster who called herself Jeanne de Valois-Saint-Rémy, also known as Jeanne de la Motte, created a plan to use the necklace to get rich and possibly power and royal honors. In March 1785, Jeanne became the mistress of the Cardinal de Rohan, a former French ambassador to the court of Vienna. 

The Cardinal was hated by Queen Marie Antoinette for having spread rumors about the Queen's behavior to her mother, the Holy Roman empress Maria Theresa. The Queen had also learned of a letter in which the Cardinal spoke of Maria Theresa in a manner that the Queen found offensive.

At this time, the Cardinal was trying to get the Queen's to like him again so that he could become Prime Minister of France. Jeanne de la Motte persuaded Rohan that she had been friends with the Queen. After hearing this, Rohan used Jeanne to get the Queen to like him again (though he did not know that Jeanne was lying to him). Jeanne promised the Cardinal that she will get the Queen to like him.

The affair began after Jeanned continued to send fake letters to the Cardinal pretending to be Marie Antoinette. After Rohan fell in love with Antoinette as he believed she was falling in love with him, he wanted to meet her. In the gardens of the Palace of Versailles, the Cardinal met with a woman he believed to be Marie Antoinette. In fact, the woman was a prostitute, Nicole Le Guay d'Oliva, whom Jeanne had hired because of her resemblance to the Queen. 

Jeanne took advantage of lying to Rohan by asking a lot of money. 

On 21 January 1785, Jeanne told the Cardinal that Marie Antoinette wanted to buy the necklace; but, not wishing to purchase such an expensive item publicly during a time of need, the Queen wanted the Cardinal to act as a secret buyer. A little while later, Rohan negotiated the purchase of the necklace for 2,000,000 livres. Rohan took the necklace to Jeanne's house, where a man, whom Rohan believed to be a valet of the Queen, came to fetch it. The diamond necklace “was picked apart, and the gems sold on the black markets of Paris and London” by Madame de la Motte.

Aftermath
When Marie Antoinette found out about this, she had Rohan arrested publicly. When this happened, Jeanne had left the town but was arrested afterwards. 

Cardinal Rohan and Jeanne de la Motte were found guilty. Rohan was sentenced to strip his honors and ambassador jobs and in exile. Jeanne was sentenced to be whipped, branded and in jail. However, she escaped jail and took refuge in London.

In popular culture

Many books and other works have shown the Affair of the Diamond Necklace:

The Affair of the Necklace a 2001 movie with Hilary Swank and Joely Richardson
The Affair of the Diamond Necklace is in the anime The Rose of Versailles
Puppet History talked about the Affair of the Diamond Necklace in the episode "Stealing the World's Most Expensive Necklace."

References

1784
1785