The 163.41-carat flawless D colour diamond, suspended from an emerald and diamond necklace called The Art of Grisogono, sold for 33.5 million Swiss francs ($33.8 million, 28.7 million euros), after taxes and commissions, at the Christie's autumn jewel auction.
This marks "a new world-record price for a D colour diamond at auction," Rahul Kadakia, auctioneer and head of Christie's international jewels division, told AFP.
D is the highest colour grade attributed to a diamond, indicating that the stone is completely colourless, and thus extremely rare.
With a drawn-out round of rapid-fire bidding starting at 20 million francs, the necklace was finally sold to a telephone bidder, who wished to remain anonymous, for well above the asking price of 25 million.
But some had expected The Art of Grisogono, which Christie's described as a "masterpiece of unparallelled beauty and exquisite workmanship", to fetch even more.
"I am disappointed that the Art of de Grisogono didn't sell for a more dazzling price," said Tobias Kormind, head of 77 Diamonds, a large European online diamond jeweller, who had said before the sale he thought the price might top $50 million.
The flawless, D colour 11A type diamond was cut from a 404 carat rough rock which was discovered in February 2016 in the Lulo mine in Angola -- the 27th biggest rough white diamond ever discovered.
The rough was analyzed in Antwerp and cut in New York, where a team of ten diamond-cutting specialists were involved in mapping, plotting, cleaving, laser-cutting and polishing the giant rough rock into a polished, flawless diamond.
A team from Swiss luxury jeweller de Grisogono then created 50 different designs around the 163.41-carat diamond, before opting for an asymmetric necklace with the stone as its centrepiece.
The left side of the necklace is made up of 18 emerald-cut diamonds and the right side composed of two rows of pear-shaped emeralds.
French royal diamond
Another highlight of Tuesday's auction, a large pink diamond once set in the crowns of numerous French kings and emperors, including Napoleon, meanwhile sold for far more than the $6-9 million estimate.
It went under the hammer, again to an unidentified telephone bidder, for 12.5 million francs, with the final price tag after taxes and commissions ticking in at 14.4 million francs ($14.5 million, 12.3 million euros).
The gem was named after Cardinal Mazarin, an Italian cardinal and diplomat, as well as a great art collector, who served as chief minister under Louis XIII and Louis XIV, and who bequeathed it and other diamonds to the Sun King in his will.
The pink stone, originally dug out of the ancient mines of Golconda in south-central India, sparkled on the crowns of Louis XV and Louis XVI, who was guillotined during the French Revolution.
And it graced the crown of Napoleon I, Napoleon III and Empress Eugenie, among others.
It has since passed through the hands of famous French jeweller Frederic Boucheron and later the Baron von Derwies.
Christie's said the seller was a private collector, but did not reveal their identity.
Tuesday's sale marked the first time the diamond appeared at auction in 130 years.
It has been auctioned off once before: It was among the French Crown Jewels sold off in 1887 -- 17 years after France's Second Empire collapsed and Napoleon III and his wife Emperess Eugenie sought exile in England, leaving their jewels behind.
Christie's jewel auction, which raked in sales totalling 105.4 million Swiss francs, will be followed on Wednesday by a similar auction at Sotheby's.
The highlight of that show, also in Geneva, will be The Raj Pink, the world's largest known fancy intense pink diamond, which Sotheby's is aiming to sell for $20-30 million.