The diamond was unearthed back in November by Meya Mining, a company jointly owned by Namibia-based conglomerate Trustco Group and Germinate Sierra Leone.
According to Graff, the Meya Prosperity Diamond is the 29th largest diamond ever uncovered and the 5th largest from Sierra Leone. It was buried in the same ground where the 709-carat Peace Diamond, which the jeweller bought for $6.5 million, was discovered.
With this latest purchase, Graff Diamonds has acquired the majority of the top 21 largest stones of the 21st century.