The Lesotho Promise - one of the world's largest diamonds - has been sold in the Belgian city of Antwerp for US$12.4m (£6.7m).
The diamond, an uncut, 603-carat white gem, weighing 120g (4.2oz), was found in Lesotho on 22 August.
The buyers have been identified as the South African Diamond Corporation.
The diamond - about the size of a golf ball - is said to be the 15th largest ever discovered. It will be cut into one large and several smaller stones.
The Lesotho Promise was found in the Letseng mine, which is jointly owned by the Gem Diamond Mining Company of Africa and the Lesotho government.
It is the biggest uncut diamond discovered since the Millennium Star, at 777 carats, was found in the Democratic Republic of Congo in 1993.
But the largest diamond recorded is the Cullinan, found in 1905 in South Africa, which had a weight of 3,106 carats.
The 530-carat Star of Africa was cut from it and now forms part of the British crown jewels displayed in the Tower of London.