The world's largest flawless fancy vivid blue diamond is expected to fetch up to £15m when it goes on sale at Christie's next month.
Christie's New York has proudly displayed 'The Blue', the magnificent 13.22 carat diamond which will headline the upcoming sale in Geneva.
Experts predict it will fetch an eyebrow-raising sale price of between $21m (£12.5m) and $25m (£15m).
Rahul Kadakia, Head of Jewellery for Christie’s Americas & Switzerland, said: "To have a stone that weighs 13 carats is near impossible.
"The stone is internally and externally bereft of any imperfections... in simple terms, it's the best blue diamond in the world."
Blue diamonds are extremely rare and make up less than two per cent of the world's diamond production.
Like most blue diamonds, 'The Blue' is thought to have been mined in South Africa.
Christie's would not reveal the owner of the jewel, but said it had been in the owner's possession for a long time.
The auction house said the owner approached them after seeing several coloured diamonds fetch record prices in recent sales.
In November Sotheby's auction house sold a plum-sized diamond, known as the Pink Star, for a record £51.7m.
A month earlier Sotheby's sold a "flawless" white diamond for a record £19m.
'The Blue' will be auctioned at the Geneva Magnificent Jewels Sale on May 14 alongside the 'The Ocean Dream' diamond.
According to Christie's 'The Ocean Dream' is the largest fancy vivid blue-green diamond in the world. At 5.5 carat, it is expected to fetch between £4.5m and £6m.
Also on sale is the exotic 'The Rajah' diamond, which is thought to have purchased from India by Tiffany & Co in the 19th Century. It is estimated to sell for between £1.8m and £3m.
Christie's has said it hopes the sale will raise in excess of £60m.