Diamond Necklace, The Affair of - shiny carbon assists in downfall of a monarchy

The Affair of the Diamond Necklace is actually a rather gripping tale. I suggest just clicking through and reading it in its entirety, but I'll try to summarize it.

Louis XVI of France ordered a super expensive necklace (Britannica says 1,600,000 livres. Wikipedia says 2,000,000 livres.) for a woman he was infatuated with. Then he died of smallpox and she was banished from court. It hadn't been paid for yet, so the jewelers tried to sell it to the new Queen, Marie Antoinette, but she refused.

A con artist Countess de la Motte (Britannica describes her as an adventuress) conceived of a plan. She became the mistress of Cardinal de Rohan who was in bad grace with the Queen. He was trying to regain the Queen's favour and was excited when la Motte mentioned that she enjoyed the Queen's goodwill.

A fake correspondence began between Rohan and the Queen. The letters were forged, but they convinced Rohan that the Queen was in love with him. He asked to meet with her, so la Motte arranged a meeting between Rohan and a prostitute dressed up to look like the Queen.

Taking advantage of all this, la Motte borrowed large sums of money from Rohan, supposedly for the Queen's charity work. She used the money to work her way into respectable society, all the while claiming she knew the Queen well.

The jewelers decided to use her to sell the necklace to the Queen. She eventually agreed and had several fake letters from the Queen sent to Rohan, ordering him to buy the necklace. He got the necklace in exchange for agreeing to pay in multiple payments. The necklace was given to la Motte's husband who pretended to be a valet of the Queen. He then took it to London where it was broken up and the diamonds sold individually.

The jewelers eventually complained to the Queen directly about not receiving payment. The Queen knew nothing of this and as a result, all sorts of things blew up. Lots of people were arrested by the King and the whole thing was made very public. The populace was enraged that the Queen would spend so much money on something so frivolous when things were going so poorly for everyone else. This was despite the Queen's actual innocence in the matter

This degraded the Queen's reputation quite a bit and assisted in the eventual downfall of the monarchy during the French Revolution.