The stone was a 115ct top white colour type 2a diamond.
Others found this year included the Lesotho Legend, an exceptional quality 910ct D colour Type 2a diamond, which was the second largest diamond recovered in the past century and the largest recovered at Letšeng to date. It was sold in March for US$40 million.
Others recovered included top white colour type 2a diamonds of 169ct and 152ct and D colour Type 2a diamonds of 149ct, 117ct and 110ct.
The tally of over-100ct diamonds for this year so far is already above the seven large stones recovered during the whole of 2017.
Gem CEO Clifford Elphick previously chalked the climbing volume of large over-100ct stones to a reduction in the outer feed through the plant, as well as keeping the plants running at a steady rate.
Gem;s shares were up 2.27% Tuesday to £1.125 (US$1.515) per share.