If David Beckham is wondering what to get Victoria for Christmas, then we may have found the answer. A stunning bright yellow 100-carat diamond was unveiled for the first time to the world in London yesterday. The gem is so rare that experts estimate it could be worth as much as £13 million. Currently the stone, which is around an inch square and three-quarters of an inch deep, is on a pendant. But for those who like their jewellery to be exceptionally eye-catching, it could even be made into a ring. The stone named the 'Dream Diamond' is being sold by the Graff diamond company, which says it is likely to be bought by a gem collector, investor, or a celebrity. Most diamonds are clear, however occasionally the combination of heat and pressure that forms the stone along with certain minerals in the rocks, can produce coloured versions. Purple, blue, pink, yellow, green and red diamonds all exist, although they are extremely rare. Because this stone is a particularly vivid colour it makes it more unusual than other rare 'canary yellow' diamonds. There are also very few diamonds of such enormous size. The diamond, which came from South Africa, was first seen when still in its rough stage by Laurence Graff who owns the London-based jewellery company that bears his name. Mr Graff, who is known as the 'King of Diamonds' was said to be mesmerised by its unusual hue and colour and so bought it. 'He knew it would turn into the most exceptional diamond he had ever seen,' said Graff marketing manager Fiona Spence. The stone was then sent off to the Gemological Institute of America for testing to show that it was entirely natural. When confirmation of this came, he sent the 190.72 rough crystal off to his master cutter Antonio Bianco to be turned into a glittering gem. Mr Bianco, also known as Nino, said the next nine months were a 'relentless process of total engagement, commitment and endless manoeuvring' to cut the diamond. Thanks to his skill, the brilliance of the yellow diamond was revealed. The 'cushion cut' stone was unveiled yesterday by Graff at Kensington in London, and is now being offered for sale. Anyone interested in purchasing it is advised to contact the company directly. Coloured diamonds have proved hugely popular among celebrities in the past. Sir Elton John, Jennifer Lopez and Victoria Beckham all have pink diamonds. Meanwhile supermodel Heidi Klum received a heart-shaped canary yellow diamond from husband Seal. One of the most famous and valuable yellow diamonds is the Tiffany Diamond, which is still on show in the Fifth Avenue flagship store in New York. The 287.42 carat stone was acquired by Charles Tiffany from the Kimberley Mines in 1878.