An “extremely rare” fancy vivid pink diamond weighing 8.72 carats sold for $15.9 million at the spring Magnificent Jewels and Nobel Jewels auction.

The stone, known as “The Historic Pink” and mounted on a ring with a classic non-modified cushion cut, is believed to have been part of the collection of Princess Mathilde, niece of French Emperor Napoleon I, according to the Gemological Institute of America.

Another of its former owners was the reclusive American heiress and philanthropist Huguette Clark, who died in 2007. It only recently reappeared after having been kept in the safe of a bank since the 1940s.

The origins of the stone remain unclear. The technical characteristics of the stone and the fact that it is so old suggest it may have been found in the famous Golconda mines of India, according to David Bennett, head of Sotheby’s international jewellery division.