The “Bleu Royal” diamond. (Photo: Denis Balibouse/Reuters)

At 17.6 carats, the vivid blue diamond, known as “Bleu Royal” and set in a ring, is among the rarest ever to be unearthed.

Christie’s said the diamond was unique because of its a deep rich blue colour and its unmodified pear brilliant shape.

In a separate sale, Christie’s sold a Rolex wristwatch worn by Marlon Brando in the 1979 movie “Apocalypse Now” for nearly 5 million USD.