Graff, which has cut and polished some of the largest diamonds ever found, on Wednesday evening unveiled the world’s largest square emerald cut diamond weighing 302.37 carats.
The original rough diamond was found at the Lucara Karowe mine in Botswana in 2015 – at the time the largest gem quality rough diamond discovered in more than 100 years.
The record-breaking stone was named Lesedi La Rona, meaning "Our Light" in Tswana.
Graff founder Laurence Graff said in a statement on Wednesday: "There is a huge amount of good fortune involved in unearthing a rough diamond of this extraordinary beauty and importance. Year after year can go by… month after month can pass… with nothing… then you get lucky."
From discovery to completion, the process of analysing, cutting and polishing took more than 18 months.
The company said it was the largest, highest colour, highest clarity diamond ever graded by the Gemological Institute of America, making it one of the "greatest diamond achievements in history".
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