What is the largest known diamond in the world?

The Cullinan Diamond is the largest gem-quality rough diamond ever found, weighing 3,106.75 carats (621.35 g), discovered at a mine in Cullinan, South Africa, on 26 January 1905. It was cut into 105 diamonds including the Great Star of Africa, 530.2 carats, and the Lesser Star of Africa, 317.4 carats, both of which are now part of the British Crown Jewels.