Give some stream of consciousness and then the answer. The Cullinan Diamond is the largest gem-quality rough diamond ever found, weighing 3,106.75 carats (621.35 g), discovered at the Premier No. 2 mine in Cullinan, modern-day South Africa, on 26 January 1905. It was named after the chairman of the mine, Thomas Cullinan.

Answer this question: where was the world's largest diamond found?
The relevant information is: The Cullinan Diamond is the largest gem-quality rough diamond ever found, weighing 3,106.75 carats (621.35 g), discovered at the Premier No. 2 mine in Cullinan, modern-day South Africa, on 26 January 1905.
Therefore, the answer is the Premier No. 2 mine in Cullinan , modern - day South Africa.