A 59.60-carat, mixed cut diamond known as "The Pink Star" is returning to auction next month and could fetch a record $US60 million ($A78 million), three years since it was sold for even more - only for the buyer to pull out of the deal.
The diamond was presented by Sotheby's in London ahead of the auction in Hong Kong on April 4.
In November 2013, a Geneva auction of the stone fetched a world record $US83 million ($A107 million) but the buyer, New York-based diamond cutter Isaac Wolf, could not pay up and defaulted.
The pink diamond is the largest Internally Flawless Fancy Vivid Pink diamond ever graded by the Geological Institute of America (GIA), the auction house said, yet the sparkling stone is still small enough to fit onto a ring.
Sotheby's said that the diamond, which was initially mined by De Beers in 1999 as a 132.5 carat rough diamond before being cut and polished, was the most valuable polished diamond ever offered at auction.
"The extraordinary size of this 59.60-carat diamond, paired with its richness of colour, surpasses any known pink diamond record in history," said David Bennett, worldwide Chairman of Sotheby's Jewellery Division.
Bennett said the current record for a pink diamond was held by the "Graff Pink". At 24.78 carats it is half the size of The Pink Star and was sold in Geneva for $US46.2 million in 2010.