The 17.6-carat "Bleu Royal" lived up to its pre-auction fanfare at Christie's Geneva on Tuesday as the largest internally flawless fancy vivid blue diamond ever put up for auction sold for $43.8 million after a tense, six-minute bidding war.

Two phone bidders battled back and forth in a dramatic exchange that included 21 individual offers. The bidding started at 19 million Swiss francs (about $21.1 million) and creeped forward in increments of 1 million, 500,000 and 250,000 Swiss francs.

Taking in the action in real time via streaming video, viewers around the world witnessed Christie's international head of jewelry and auctioneer Rahul Kadakia finally put the hammer down at 34 million CHF ($37.8 million). With commissions and fees included, the final price was 37.7 million Swiss francs, or $2.49 million per carat. The winning bidder remains anonymous, for now.

The realized price of $43.8 million was solidly in the range of the Bleu Royal's pre-sale estimate of $35 million to $50 million. Its strong showing elevated the diamond into the upper tier of blue diamonds that have been sold at auction. Among them are the 14.62-carat “Oppenheimer Blue” (Christie’s 2016, $57.5 million), the 15.10-carat “De Beers Blue” (Sotheby’s 2022, $57.47 million) and the 12.03-carat “Blue Moon of Josephine” (Sotheby’s 2015, $48.5 million).

Set in a platinum and 18-karat rose gold ring, the perfectly symmetrical pear-shaped Bleu Royal is flanked by a pair of pear brilliant-cut diamonds weighing 3.12 and 3.07 carats, respectively. The piece had been tucked away in a private collection for the past 50 years.

“This is a true miracle of nature,” commented Kadakia prior to the auction. “Over our 257-year history, Christie’s has had the privilege of offering the world’s rarest gems at auction, and Bleu Royal continues this tradition. We are proud to offer collectors the opportunity to own a diamond fit for royalty.”

Blue diamonds are considered one of the rarest colors of all diamonds. A fabulous fluke of nature, a blue diamond owes its color to the random presence of boron within the diamond’s carbon structure. The Bleu Royal is categorized as a Type IIb diamond, a quality level that includes less than 0.5% of all diamonds.

Scientists believe that blue diamonds form about 400 miles below the surface, four times deeper than about 99 percent of all other diamonds.

Credits: Images courtesy of Christie’s.