An exceptional 11.15-carat diamond, described by Sotheby’s as one of the “purest and pinkest” diamonds to appear at auction, is expected to sell for HK$170 million (around US$21 million) at a single-lot auction in Hong Kong. 

One of only two internally flawless fancy vivid pink diamonds of over 10 carats ever to come to auction, the Williamson Pink Star will be offered in a single-lot auction at Sotheby’s Hong Kong on October 5.

The diamond was unveiled today at Sotheby’s London ahead of a world tour, starting in Dubai, Singapore, Taipei and Hong Kong.

The Williamson Pink Star is only outsized by the record-breaking CTF Pink Star, the 59.60-carat oval mixed-cut diamond, which sold at Sotheby’s in April 2017 for US$71.2 million. CTF Pink still holds the world auction record for any diamond, gemstone or jewel.

A natural wonder of nature, this cushion-shaped stone to be offered on auction was named in homage to two legendary pinks – CTF Pink Star and the celebrated “Williamson” – a 23.60-carat diamond given as a wedding present to Her Majesty Queen Elizabeth II in 1947 by the Canadian geologist and royalist, Dr. John Thorburn Williamson, who owned the Mwadui mine in Tanzania where it was discovered. 

The discovery of a gem-quality pink diamond of any size is an extremely rare occurrence, but even more so in the past two years, with the official closure of the Argyle mine in Australia, which was responsible for the world's largest supply of pink diamonds, according to Sotheby's.