The Blue Moon of Josephine diamond has sold for $48.6m at Sotheby's Geneva, setting a new world record.
The lot led the Magnificent Jewels auction on November 11.
It beat the previous record for a diamond, set at $46.1m for the Graff Pink at Sotheby's in 2010.
At 12.03 carats, the diamond is the largest known fancy vivid blue and is internally flawless - making it extremely rare.
A Hong Kong businessman named Joseph Lau made the final bid. He also bought the pink diamond, which he named Sweet Josephine, on November 10.
He reportedly renamed both of the stones for his youngest daughter, Josephine.
Lau is a billionaire who was convicted of bribery and money laundering in Macau in 2012. He escaped his jail term by moving to Hong Kong, which has no extradition treaty with Macau.
David Bennett, Sotheby's head of jewellery, said: "The tremendous excitement last year over the discovery of a 29.62-carat blue rough diamond at the Cullinan mine in South Africa has now been proved to have been totally justified.
"Weighing in at 12.03 carats, the 'Blue Moon' diamond is a simply sensational stone of perfect colour and purity, combined with a superb cushion shape.
"Blue, for me, is the most mysterious and magical of all the colours of diamond, and the Blue Moon will now take its place among the most famous gems in the world."
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