A new colourless, pear-shaped diamond weighing 101.73 carats raked in a record 23 million Swiss francs ($23.5 million, 18.5 million euros) at a Christie's auction in Geneva late Wednesday.
The price, which does not include tax or commission, is the highest ever paid for a flawless colourless diamond, according to the auction house, which had hoped the gem would go for $30 million.
"Twenty-three million (Swiss) francs! Your last chance! Twenty-three million, sold!" Francois Curiel, the head of Christie's jewellery division shouted, clinching the deal before some 150 people gathered for the auction at a luxury Geneva hotel.
Including tax and commission, the total ticked in at $26.7 million, Christies said after the sale of the stone, which is the largest diamond in its category ever to go under the hammer.
The American Institute of Gemology has handed the gemstone the top colourless grade "D" and the best clarity grade, "flawless", which is characterised by its "absolute symmetry", according to Christies.
In the rough, the diamond was 236 carats when it was extracted from the Jwaneng mine in Botswana, before it was meticulously sculpted for 21 months, Christie's said.
Wednesday's auction marked the first time the rock goes on sale, and the buyer will have the privilege of naming it.
Wednesday's sale marked the highest price ever paid for a flawless colourless diamond at auction.
The previous auction-price record-holder in this category was the 84.37-carat Chloe round diamond, snapped up at a Sotheby's auction in Geneva in 2007 by Guess Jeans founder Georges Marciano.
A diamond merchant sold the new diamond, the centrepiece of Christie's traditional May jewellery and luxury watch sale, but it was not immediately clear who the deep-pocketed buyer was.
In the "colourless, flawless" category, the reigning world champion in terms of size is meanwhile the Cullinan Diamond, a gem weighing 530.2 carats that is part of the British crown jewels.
Last November, Christie's sold the 76-carat Archduke Joseph Diamond, in the initially flawless category a notch below flawless, on auction in Geneva for $21.5 million.
And in May 2011, a heart-shaped 56-carat diamond was auctioned off for $10.9 million.
The Elizabeth Taylor Diamond, which is in the same D-colour category but weighs in at only 33.19 carats, was meanwhile sold for $8.8 million on auction in New York in December 2011.