The flawless 'Archduke Joseph" diamond, from India's famous Golconda mines, broke several world records when it was sold at auction in Geneva late Tuesday for $21.47 million (16.9 million euros).
The price which the 76 carat jewel fetched at the Christie's sale is a record for the auction of a clear, colourless diamond.
It is also the highest auction price per carat for such a gem and the record for a Golconda diamond, the same mines which produced the Koh-i-Noor which adorns the British Queen's crown.
"It's a cushion-shaped diamond, weighing 76.02 carats, of D colour" the purest, most colourless variety of diamond, a rarity and a speciality of the ancient Golconda mines in the Indian state of Andhra Paradesh, said Christie's jewelery expert Jean-Marc Lunel.
The 'Archduke Joseph,' which was bought by an anonymous bidder, once belonged to the Habsburgs, former rulers of the Austrian empire.
It takes its name from the Archduke Joseph (1872-1962) who was for a short period the Hungarian head of state.
The diamond was sold in 1936 to a still-anonymous buyer and, hidden in a safe, escaped the attentions of the Nazis during the Second World War .
It reappeared on the international scene at a sale in London in 1961.
In the 1990s it was sold again, in Geneva, for $6.5 million.