The De Beers Cullinan Blue is an extraordinary 15.10-carat step-cut blue that has been recently cut from an exceptional rough stone discovered in 2021. It’s now the star of a stand-alone, single lot live auction happening in late April this year and estimated to fetch HK$380 million. In its newly formed state, the piece is now the largest vivid blue diamond to appear at auction and the largest internally flawless step-cut vivid blue diamond that the Gemological Institute of America (GIA) has ever graded.

Blue diamonds of this importance are exceptionally rare, with only five 10-carat plus examples ever having come to auction and none of which have exceeded 15 carats. The appearance of the De Beers Cullinan Blue is a landmark event itself. The auction will be part of Sotheby’s Hong Kong Luxury Week and given the global interest in the diamond, it will be showcased on a worldwide tour. It’s currently in Sotheby’s galleries in New York and will then travel to cities such as London, Dubai, Singapore, Shanghai, Beijing, Shenzhen and Taipei.

“Blue diamonds of any kind are rare on the market, but this is the rarest of the rare; nothing of remotely similar calibre has appeared at auction in recent years. Hundreds of millions of years in the making, this extraordinary blue diamond is surely one of nature’s finest creations,” says Patti Wong, the chairman of Sotheby’s Asia.

The diamond was first discovered at the Cullinan mine in South Africa in 2021, one of the very few sources in the world for extremely rare blue diamonds. Over the past year, De Beers worked with its partner, Diacore, to cut and polish the rough diamond and bring the De Beers Cullinan Blue to life.

Blue diamonds are among the rarest of all coloured diamonds as their colour is usually caused by the presence of trace amounts of the rare element, boron within the diamond crystal lattice. There’s also the fact that there are very few sources in the world for blue diamonds. Most are recovered from the Cullinan mine including many of the world’s most famous diamonds such as the 530-carat Great Star of Africa which has the largest faceted colourless diamond in the world.