The Blue Moon, a 12.03 ct. internally flawless vivid blue cushion cut, fetched $48.5 million at the Sotheby’s Nov. 11 sale in Geneva, earning it a place in the record books as the most expensive diamond ever sold at auction.

The sale also set a price-per-carat record for a gemstone: $4.02 million per ct.

The final price falls within the stone’s $35 million–$55 million estimate. It tops—though not significantly—the previous record held by the Graff Pink, the 24.78 ct. fancy intense pink, which sold for $46.1 million in November 2010. (Three years later, the Pink Star temporarily broke that record with a hammer price of $83 million. That sale was canceled soon after.)

The stone’s buyer was a private collector from Hong Kong who changed its name to the Blue Moon of Josephine. It was not clear at press time if the buyer is the same Asian private who bought the top lot at a Christie’s auction on Nov. 10 and named it the Sweet Josephine. (UPDATE: It is the same buyer, who has been identified as Joseph Lau.)

The Blue Moon is among the few blues with a fancy vivid grade—the highest rating for a colored diamond. The stone comes from a 29.62 ct. piece of rough discovered by Petra Diamonds at the Cullinan mine in South Africa in January 2014. It sold for $25.6 million a month later to New York City–based Cora International, which then spent six months cutting and polishing it.

“Even among this extremely rare class of blue diamonds, to find one vivid blue diamond that is more than 12 cts. and internally flawless, really only happens once in a blue moon,” said Cora owner Ehud Laniado in a statement. “It took Cora experts five months to assess the rough stone originally unearthed from the Cullinan mine in South Africa. They then created 30 models of the diamond and cut each one differently until they achieved the perfect result. It took three more months to bring the Blue Moon diamond to its ultimate spectacular shape using advanced technology and sophisticated tools.”

The auction also set a world record for a fancy orangey pink diamond. The 15.2 ct. VS2 clarity stone, from the collection of Sir Sean Connery, sold for $4.04 million, or $266,063 a carat.

The overall sale netted $139.1 million.

(Courtesy Sotheby’s)

Rob Bates

JCK News Director