In the world of most expensive diamonds, one variety which is sought after by collectors, are the blue diamonds. Some of these have managed to break records during their sale, including the likes of Bulgari $2.9 million blue diamond ring, the Bvlgari vivid blue diamond, and De Beers Millenium Collection diamond. One other such precious blue diamond, happened to the 1965 Bulgari circa ring, which was expected to sell at around $2.3 million at a Bonham’s auction. The diamond has finally been sold, but for a many times the expected price to finally bring in £6.2 million ($9.49 million) at Bonham’s Fine Jewelry sale in London. The price tag also puts the 5.30 blue diamond ring to be the most expensive diamond on a per carat basis. The buyer is known to be Graff Diamonds, one of the world’s best known collector houses of the precious stone.