The colourless diamond was taken from a 404-carat stone found in Angola.
Sotheby’s plans to sell the ring at the Magnificent Jewels auction at the Four Seasons Hotel des Bergues in Geneva on Wednesday. The item is expected to fetch at least $30m (£23m) at auction.
The rough was analysed in Antwerp and cut in NY, where a team of 10 diamond-cutting specialists were involved in mapping, plotting, cleaving, laser-cutting and polishing the giant rough rock into a polished, flawless diamond.
Previously, Christie’s set an auction record in May 2016 with the sale of a 14.62-carat diamond known as the “Oppenheimer Blue” for $50.6m (£34.7m). The stone was the largest of its kind ever auctioned.
The necklace is made of 18 diamonds on one side and two rows of pear-shaped emeralds on the other.
Unsurprisingly it comes with a hefty price tag.
Tuesday’s sale marked the first time the diamond appeared at auction in 130 years. Originally from the Golconda mines in India, the stone was set in the crowns of nearly all kings and emperors of France since the early 18th century, Christie’s said.
A flawless 163-carat clear diamond fetched about $US34 million ($49.4 million) at Christie’s in Geneva.