The second-largest diamond ever excavated has been found in a mine in Botswana.

The fist-sized stone has been measured at 2,492 carats, placing it second only to the Cullinan Diamond found in South Africa more than a century ago.

Experts have yet to fully grade the champagne-coloured rough diamond, but Lucara, the company that owns the mine, has described it as “high-quality”. Industry sources told The Telegraph it could fetch as much as £53 million.

The unnamed stone is due to be presented to the world at the office of Mokgweetsi Masisi, Botswana’s president, on Thursday. It is likely to be sold to a large jewellery or fashion house.

Discovery of the diamond marks another success for Lucara’s Karowe mine, which has found four of the world’s largest stones since it opened in 2012.

The Canada-based diamond miner has been using X-ray technology to pinpoint large diamonds and unearth them without breaking them up.

William Lamb, Lucara’s chief executive said: “We are ecstatic about the recovery of this extraordinary 2,492 carat diamond.

“This find not only showcases the remarkable potential of our Karowe Mine, but also upholds our strategic investment in cutting-edge XRT technology.”

The diamond is understood to have been found in an open caste section of the mine.

Excitement around the “epic” diamond will be welcome in an industry that has struggled to compete with lab-grown stones.

Prices of synthetic diamonds have plummeted in recent years, eating into the market share and profits of diamond miners.

“For the diamond mining sector, this discovery is a stand out moment,” said one source.

The largest diamond ever unearthed was the Cullinan Diamond discovered in South Africa in 1905.

The Cullinan was 3,106 carats and was cut into gems, the two largest, the Great Star of Africa and the Lesser Star of Africa, are set in the Crown Jewels.

A bigger black diamond was discovered in Brazil in the late 1800s, but it was found on the earth’s surface and was believed to have been part of a meteorite.

Recent large finds at the Karowe mine include the Sewelô diamond, found in 2019, which was recognised at the time as the second-biggest mined diamond in the world at 1,758 carats.

It was bought by French fashion house Louis Vuitton for an undisclosed amount.

The 1,111-carat Lesedi La Rona diamond, was found in the mine in 2015 and bought by Graff, the British jeweller, for $53 million (£40 million) in 2017.