An internally flawless vivid blue diamond weighing 7.03 carats has sold for a record 10.5 million Swiss francs in Geneva.
The perfect stone is the rarest to enter the international market this year.
It was sold on Tuesday by Sotheby's auction house.
The diamond was sold after a tense battle between two telephone bidders. The winner will have the right to name the stone.
The blue diamond is mounted in a platinum ring and was extracted last year from the Cullinan mine in South Africa.
The previous record price for a blue diamond was $US7.9 million in 2007.