A record blue diamond co-owned by De Beers far outstripped its presale estimate in a stand-alone sale at Sotheby’s in Hong Kong, garnering HKD 450.9 million ($57.5 million).

The step-cut, 15.10-carat, fancy-vivid-blue, internally flawless stone, called the De Beers Cullinan Blue, is the largest of its color to appear at auction. The stone sold to an unnamed buyer following a “prolonged, eight-minute battle between four contestants,” Sotheby’s said Wednesday.

The price achieved is a tie with the current record holder for a blue diamond, and also makes the stone the third most valuable diamond of any color to sell at auction, Sotheby’s explained. The stone had been expected to fetch up to $48 million.

“The De Beers Blue captivated me from the moment I laid eyes on it,” said Patti Wong, chairman of Sotheby’s Asia. “With its powerful vivid color, and breathtakingly beautiful cut, it is truly a once-in-a-generation stone, and quite simply the greatest blue diamond of its size I have ever seen during my 31-year career at Sotheby’s.”

Petra Diamonds discovered the 39.35-carat rough in April 2021 at its Cullinan mine in South Africa. In July, De Beers and Diacore bought the stone for $40.2 million, and Diacore manufactured the piece into the final polished.