Weighing 12.03 carats, a blue diamond termed internally flawless by the GIA -- discovered in South Africa over a year ago -- could sell for a record $55 million at Sotheby's this fall.

Dubbed the Blue Moon diamond, the buzzworthy stone will tour Hong Kong, London and New York before hitting the auction block in Geneva on November 11.

"The Blue Moon diamond is a simply sensational stone of perfect colour and purity," David Bennett, head of Sotheby's international jewellery division, said in a statement

Blue Moon is the largest cushion-shaped stone graded  as a fancy vivid blue diamond to ever appear at auction. The GIA Monograph notes the singularity of the gem's spectacular blue, which “could be indescribable to even the most experienced diamantaire or colour theorist; some, however, liken it to the ocean”.

If the higher end of the $35-$55 million estimate is achieved, the Blue Moon would be a diamond record-setter. But it would need to outperform the Graff Pink sold in November 2010. That 24.78 carats pink diamond brought just over $46 million.

In November 2014, a 9.75 carat blue diamond fetched $32.6 million at auction, setting the current record for the category.

Diamond specialists Cora International bought the uncut Blue Moon last year for a reported $26 million. "The fact that you could buy it rough, plan it and cut it is special,” said Suzette Gomes, CEO of Cora International to Forbes. “This is a billion years old and it’s going to be here long after we’re gone. That’s the beauty of diamonds.”