Oct. 9 (Bloomberg) -- Graff Diamonds, whose jewelry has been worn by Paris Hilton and Oprah Winfrey, paid $12.4 million for the Lesotho Promise, the biggest diamond found in 13 years.

The 603-carat gem found at the Letseng mine in Lesotho was sold by tender in Antwerp, Gem said today. It's the biggest found since the 777-carat Millennium Star, owned by De Beers, was discovered in the Democratic Republic of Congo in 1993. The Lesotho Promise is a so-called white or type-D diamond, the best grade.

``We are delighted with the price achieved for this historically significant stone,'' Clifford Elphick, chief executive officer of closely held, Johannesburg-based Gem, said in an e-mailed statement.

The world's biggest uncut diamond was the 3,106-carat Cullinan found at Premier mines in South Africa in 1905. That stone produced the 530-carat Star of Africa, the second-largest cut diamond in the world, which lies in the scepter of the British royal family in the Tower of London. A carat is equal to a fifth of a gram.

Graff, based in London and founded by Laurence Graff, boasts on its Web site that it sells ``the most fabulous jewels in the world.''

The company lists 13 locations where it sells its gems, including the The World, a residential ocean liner that circumnavigates the globe. Celebrities including Oprah Winfrey, Victoria Beckham, Kylie Minogue, Naomi Campbell and Paris Hilton are pictured on its Web site wearing Graff diamonds.

As Many as 40 Buyers

Diamonds cut by Graff include the 137.8 carat Paragon and the 40 carat Sun King. Executives at Graff weren't available to take calls when called by Bloomberg.

Graff beat bids from Antwerp's Rosy Blue Group, Alain Sternberg Bvba and Omega Diamonds, with as many as 40 potential buyers viewing the stone.

The winning bid was announced by Mamphono Khakethla, Lesotho's minister of natural resources, at the World Diamond Centre.

Diamonds occur in colors including black, brown, blue, yellow and pink with clear diamonds being the most valuable. The Lesotho Promise is the 15th-biggest ever found.

Elphick is the former managing director of E. Oppenheimer & Son, the company that runs the investments of the Oppenheimer family. They own 40 percent of De Beers, the world's biggest diamond company.

Famous Diamonds

On June 27, Gem agreed to buy a 76 percent stake in Letseng for 879.5 million rand ($112 million). The company is considering doubling the size of the mine, Elphick said June 29.

The deposit at Letseng, the country's sole source of gems and the world's highest diamond mine, was discovered in 1957 and mined by De Beers between 1977 and 1982. Its full name is Letseng-la-Terae, which means ``the swamp in the corner'' in the Sotho language.

The diamond is bigger than the 601-carat Lesotho Brown, extracted in 1967 from the mine.

Other famous diamonds include the Steinmetz Pink, the yellow Incomparable and the 616, an uncut 616-carat diamond crystal, the largest of its kind, according to the Web site of the U.K.'s Natural History Museum

An enclave within South Africa, Lesotho is a mountainous kingdom founded around 1820 by Moshoeshoe, who gathered peoples fleeing attacks by Zulu warriors and fought wars with South Africa's British and Afrikaner settlers before the country became a U.K. colony. It won independence in 1966.

The country's income comes from textiles, tourism, money sent home by Basotho mine workers in South Africa and from Angora goats, whose coat is used to produce Mohair.

To contact the reporter on this story: Antony Sguazzin in Johannesburg asguazzin@bloomberg.net

Last Updated: October 9, 2006 10:35 EDT