The Unique Pink, a 15.38-carat vivid pink diamond, the biggest of its kind to go on auction, was sold for a record US$31.56 million (S$43 million) by auction house Sotheby's on Tuesday in Geneva, Switzerland.

The top bidder was a private individual from Asia. The seller was New York-based Cora International. The value of the "exceptional" pear-shaped diamond had been estimated at between US$28 million and US$38 million.

It was discovered less than five years ago in a South African mine. It was certified as a fancy vivid pink diamond, the most sought-after colour in pink diamonds, by the Gemological Institute of America.