A huge gem stone which could become the largest polished round diamond in history has been discovered.
The massive stone is the 20th largest rough diamond ever found, weighs 478 carats and is said to be of outstanding clarity.
It was recovered earlier this week at the Letseng Mine, in Lesotho, a small kingdom in South Africa.
Another similar sized rough stone from the same mine was recently valued at $12million.
But the clarity and round shape of the new gem mean it could be worth considerably more and in its polished state could fetch tens of millions of pounds.
It is estimated to be capable of producing a 150 carat polished gem stone, dwarfing the Koh-i-Noor diamond which is part of the Crown Jewels.
A spokesman for Gem Diamonds, who own the mine, added that initial examination suggested that the white diamond, which has yet to be named and valued, has a completely flawless centre.
The mine, which was owned by famous diamond company De Beers for many years, has already produced three of the world's biggest diamonds including the 603 carat Lesotho Promise, the 493 carat Leteng Legacy and the 601 carat Lesotho Brown.
Clifford Elphick, chief executive officer of Gem Diamonds, said 'Preliminary examination of this remarkable diamond indicates that it will yield a record breaking polished stone of the very best colour and clarity.'
The find is still dwarfed by the Cullinan Diamond which was discovered in 1905.
At 3,106 carats it was the largest gem-quality rough diamond ever found but the biggest polished stone produced from it, the Great Star of Africa - 530 carats - is a teardrop shape.
The Koh-i-noor is a round cut but at 105 carats it is smaller than the potential size of the new find.
It originated in India but was seized by Britain as a spoil of war in 1849. It supposedly brings good luck to female owners and misfortune or death to any male who wears or owns it.