In 1772, Louis XV of France commissioned the extravagant necklace for his love interest, Madame du Barry. He died before the necklace was completed. There were several unsuccessful attempts to sell it to Marie Antoinette. Marie Antoinette was blameless in the matter, but the public continued to believe gossip of her involvement.
IMAGE of Necklace: By Château de Breteuil - Wikipedia, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=76856531