Tipping the scales at an astounding 101.73-carats, it's the largest flawless diamond ever to be offered at auction. The yet-unnamed pear-shaped gem is expected to set auction records when it fetches upwards of $20 million at Christie's Magnificent Jewels sale at the Four Seasons Hotel des Bergues on May 15. Discovered in the Jwaneng mine in Botswana, the once-in-a-generation marvel weighed 236 carats in its rough state. According to The Sun, expert diamond cutters worked on the specimen for 21 months. According to a spokesperson for the auction house, the diamond was literally "sculpted like a work of art." The cutters lost nearly 57 percent of the diamond's weight during the process, but yielded a D-color, Type IIA flawless gem — the best ratings for color and clarity. “This diamond is, in its scale, quality and rarity, one of the most beautiful ‘white’ diamonds Christie’s has ever had the honor of offering for sale,” said Rahul Kadakia, Head of Jewellery, Christie’s Switzerland and Americas. How does the unnamed 101-carat diamond stack up against the largest gem-quality diamonds of all time? The reigning champ is the 530-carat Cullinan I (also known as the Great Star of Africa), which is part of the British Crown Jewels.