Rare five carat deep blue diamond ring goes under the hammer for £1.5MILLION Diamond weighs 5.30 carats and is in a Trombino ring by jeweller Bulgari Ring made in 1965 is estimated to fetch up to £1.5m on April 24 in London World-record price for a fancy deep-blue diamond is £686,000 per carat A rare deep-blue diamond ring worth up to £1.5million could make history when it goes on sale. The "fancy" diamond - which will go under the hammer later this month - weighs 5.30 carats and is set in a Trombino ring made by renowned Italian jeweller Bulgari, who is favoured by Hollywood film stars. The term "fancy" is used to describe a diamond of intense colour, and the colour "fancy deep-blue" is one of the rarest in the world. Sparkling: A Bonhams employee in London places a 5.3 carat fancy blue Diamond onto an auctioneer's Gavel Beautiful: The cushion-shaped diamond is set within a mount of brilliant-cut and baguette-cut diamonds The cushion-shaped diamond is set within a mount of brilliant-cut and baguette-cut diamonds. Blue diamonds are structurally very pure and account for less than 1 per cent of all diamonds mined. The ring is thought to have been made in 1965 and is estimated to fetch up to £1.5million at Bonhams Fine Jewellery sale in Mayfair, central London, on April 24 at 2pm. The world-record price for a fancy deep-blue diamond is £686,000 per carat but, according to staff at Bonhams, the Bulgari ring has the potential to break this. Impressive: The 'fancy' diamond weighs 5.30 carats and was set in a Trombino ring made by jeweller Bulgari Jean Ghika, director of the jewellery department, said: "There have only been 30 diamonds of this size and colour that have come up for sale globally over the last 10 years, which is a fraction of the percentage of white diamonds that have been sold during the same period of time. 'There are a number of people who are interested in this kind of stone because they don't come on the market very often' Jean Ghika, Bonhams jewellery director There are a number of people who are interested in this kind of stone because they don't come on the market very often. It attracts connoisseurs, collectors and people who just simply want to wear it because it's a wonderful stone. In September 2011 Bonhams sold a fancy vivid-blue diamond ring by Bulgari for £1.9million. The ring, set with two pear-shaped diamonds, more than doubled the pre-sale estimate - which is why experts predict the Trombino Bulgari ring will produce another record-breaking sale.