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 USD 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 USD 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.
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.
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Today's auction marked the first time the rock goes on sale, and the buyer will have the privilege of naming it.
Today'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.
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 USD 21.5 million.
And in May 2011, a heart-shaped 56-carat diamond was auctioned off for USD 10.9 million.