The Canadian mining outfit Lucara Diamond (LUCRF) had been struggling to sell the 1,109-carat uncut stone, with a Sotheby’s auction last year failing to achieve the $70 million reserve price. Experts suggested the diamond was simply too big to allow accurate analysis of the gems it might yield.

The highest bid in that abortive auction was $61 million. So, what did Graff pay in the end? $53 million.

“Our highly skilled team of master craftsmen will draw on many years of experience of crafting the most important diamonds, working night and day to ensure that we do justice to this remarkable gift from Mother Nature,” founder Laurence Graff said 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.”

Graff already bought a fragment of the Lesedi La Rona rough earlier this year for an undisclosed amount. The smaller 374-carat diamond was originally part of the larger, but broke off during extraction. Graff described the new purchase as enabling a “poignant reunion” of the two pieces.

The Lesedi La Rona was recovered two years ago from Lucara’s Karowe mine in Botswana, which is the world’s largest source of gem diamonds. Its name means “our light” in the local Tswana language.

The stone is the largest gem-quality rough diamond to have been found in the last century, with the largest in history being the legendary, 3,107-carat Cullinan Diamond that was dug up in 1905 in South Africa.

In its statement, Graff described Lesedi La Rona as the world’s most valuable rough diamond. Lucara did sell another, smaller rough diamond for more money last year—The Constellation went for $63.1 million—but Graff told Fortune that this stone no longer qualified as the most valuable rough diamond because it has since been cut up into gems.

The most expensive diamond sale took place in April, with the cut, 59.6-carat Pink Star selling at Sotheby’s for $71 million.