The world's largest uncut diamond - roughly the size of a tennis ball - has been sold to British jeweller Graff for £40million.

Canadian miner Lucara Diamond sold the 1,109-carat gem - the Lesedi La Rona - to Graff. It was found in Botswana's Karowe mine in late 2015.

'We are thrilled and honoured to become the new custodians of this incredible diamond,' said company chairman, Laurence Graff, in a statement.

'The stone will tell us its story, it will dictate how it wants to be cut, and we will take the utmost care to respect its exceptional properties.'

This tennis ball-sized rough diamond unearthed nearly two years ago by Canada's Lucara Diamond Corp has been sold for $53 million

The 1,109-carat stone, which is the world's largest uncut diamond, was bought by high-profile British diamond dealer Graff Diamonds

Lucara confirmed the hefty price tag in a statement issued in Vancouver.

'The discovery of the Lesedi La Rona was a company defining event for Lucara,' said William Lamb, president and chief executive of Lucara.

'It solidified the amazing potential and rareness of the diamonds recovered at the Karowe mine.'

The rough diamond had previously failed to meet its reserve price of more than $70 million at a Sotheby's auction in 2016. Bidding stalled at $61 million and it was withdrawn from public view.

Graff is already the owner of a 373-carat diamond, which was bought earlier this year for a relatively cheap $17.5 million and formed part of the original stone.

The stone, named 'Lesedi La Rona' or 'Our Light' in the national language of Botswana where it was mined at Lucara's Karowe mine in November 2015, is said to be 2.5 to 3 billion years old

In reuniting these two stones, Graff has a unique opportunity to create an incredibly special suite of jewels. The stones themselves are Type IIa, as chemically pure as diamonds come, with exceptional transparency and quality.

Lesedi La Rona means 'our light' in Botswana's Tswana language.

It could be cut into smaller gems for jewellery or left whole in a private collection.

The rough diamond is second in size only to the 3,106.75 carat Cullinan, which was cut into 105 diamonds, including several British Crown Jewels.

Graff Diamonds has a long history of acquiring the precious stones in multimillion-dollar deals. In 2006, it bought the 603-carat uncut Lesotho Promise at an auction in Belgium for $12.4 million.