Bonhams London sold a rare 5.30ct, fancy deep blue diamond yesterday for $9.5 million (£6.2 million) or $1.8 million per carat to Graff Diamonds. Over four times its pre-sale estimate. The previous record was $1.68 million per carat.

The fancy deep-blue cushion cut diamond is set in a 'Trombino' ring made by Bulgari, the renowned Italian jeweller. The ring was made in 1965. The diamond is mounted horizontally, pave set with briiliant cut diamonds and channel set baguette cut diamonds.

Jean Ghika, Director of Bonhams Jewellery Department said 'We are delighted with the price it has made. It was a sensational stone which charmed everyone who viewed it prior to the sale. Blue diamonds, especially those over 5.00 carats, are extremely rare to see on the market and continue to be highly sought-after. We are honored to have handled the sale of such a unique gem.'