Diamond Necklace, The Affair of the, a notorious scandal in the court of Louis XVI of France. Cardinal de Rohan, who was out of favor with Queen Marie Antoinette, was persuaded in 1784 by Countess Jeanne de la Motte that he could regain the queen's favor by negotiating for her the purchase of a certain necklace of 500 diamonds that she wanted to acquire secretly. Rohan contracted with the jewelers to pay for the necklace in installments. When Rohan could not pay the first installment in full, the jewelers asked the queen for payment. Meanwhile the necklace, which Rohan thought was in the queen's possession, had been broken up and the stones sold in London.

Rohan, the countess, and the impostor Alessandro di Cagliostro, who was accused of being an accomplice, were arrested in 1785. Rohan was cleared of the charge of having fraudulently acquired the necklace but was banished from the court. Cagliostro was also acquitted. The countess was sentenced to life imprisonment but later escaped to England. Although the queen had played no part in the affair, the scandal confirmed the belief of many in her extravagance and frivolity.