A 72.22 carat diamond described as 'flawless' is set to go on sale in Hong Kong.Sotheby's auction house in New York said it is the third largest pear-shaped stone ever to appear at auction.The diamond is what they call 'D-colour' or 'finest white', and was cut from a stone which weighed 188.11 carats.Quek Cin Yeow, the head of the jewellery department for Sotheby's Asia, said: "Bidding will start at $10 million (£4.95m) and above."We expect it to fetch anything between $10-$13m (£6.44m), and when that happens it will go into the record books as one of the top diamonds of the world."The largest pear-shaped diamond ever sold at auction was a 100.10 carat stone called Star of the Season, sold by Sotheby's in 1995 for more than $16 million (£7.93m).The successful bidder for the new gem will be able to name it after whatever, or whomever, they want.© Independent Television News Limited 2008. All rights reserved.