A stunning Bulgari blue diamond ring has sold with tremendous results at Bonhams, setting a new world record for a diamond of its type in London yesterday (April 24).

According to Bonhams, the ring 'epitomises that golden era of elegant simplicity'

The rare "fancy deep-blue" diamond, weighing 5.30 carats and set in a "Trombino" ring made by Bulgari, sold for £6.2m ($9.4m) to international diamond house Graff Diamonds, surpassing its £1.5m high estimate by 313.3%. The record price equates to $1.8m per carat.

However, the diamond is not the largest of its kind. That title is held by the famous 45.52-carat blue Hope Diamond, which was bought by King Louis XIV in the 17th century and is now housed in the Smithsonian Natural History Museum in Washington DC.

The Bulgari ring was made circa 1965, at the height of the renowned Italian jeweller's popularity. The diamond is cushion-cut, set horizontally within a mount that is pave-set with brilliant-cut and baguette-cut diamonds.

The term "fancy" describes diamonds of a particularly deep or intense colouration, with fancy deep-blue diamonds - especially those over five carats - being extremely rare on the market. This rare colouration originates from small atoms of boron mixing with carbon during the diamond's formation, which affects the absorption of light passing through the stone.

2013 has already been a brilliant year for diamond sales, with the magnificent Princie Diamond setting a $39.3m world record at Christie's earlier this month.

On April 18, a 75-carat white diamond sold for $14.2m at Sotheby's.