Photo: A 118-carat diamond looks like this

Sotheby's is calling it the greatest white diamond to ever be auctioned.

Roughly the size of a small egg, a 118-carat white, oval-shaped diamond deemed the "magnificent oval diamond of supreme importance," will be auctioned off in Hong Kong next month for an estimated $28 million to $35 million.

The current record for a white diamond is $26.7 million, after a 101-carat stone was sold last year by Christie's in Geneva.

Sotheby's then holds the other three records for auctioning off diamonds over 100 carats in 1990, 1993 and 1995.

The stone was discovered in 2011 from deep mines in an undisclosed country in Southern Africa. In its pure, original form, the diamond was 299-carats. Sotheby's declined to provide more details on the precise location of the jewel's origins and the source of the stone. The owner, said Sotheby's, would like to remain anonymous, the auction house told reporters at a press preview.

The auction date is Oct. 7.