One of the rarest precious stones in the world is being put on show to the public in advance of a sale next month.
The fancy vivid blue diamond is expected to fetch between £4 million and £6 million at Sotheby's Magnificent Jewels sale in Geneva on May 12.
The gem, described as cushion-shaped and internally flawless, owes its distinctive colour to the presence of the chemical element boron during the stone's formation.
It was discovered last year at Petra Diamonds' Cullinan diamond mine in South Africa.
The diamond is currently being seen in an international travelling exhibition and will be on show until Tuesday at Sotheby's in New Bond Street, central London.
David Bennett, chairman, Europe and the Middle East, Sotheby's international jewellery department, said: "Blue diamonds are among the rarest of all nature's treasures and it is very exciting to have such a fine example as the centrepiece of our forthcoming Geneva Magnificent Jewels sale.
"This stone certainly ranks among the most important blue diamonds that I have had the privilege of offering for sale in my career at Sotheby's.
"What makes it particularly special for us is that we've been able to follow its production from the initial rough state through the various stages of its cutting and polishing."
