'Perfect' Archduke Joseph diamond sells for $21m

One of the world's most admired diamonds has been sold at auction for more than 20m Swiss francs ($21m; £13m).

The 76-carat Archduke Joseph diamond was sold to an anonymous bidder by the Christie's auction house in Geneva.

The winning bid was 18.1m Swiss francs, and with the buyers' premium, the bidder will pay more than 20m Swiss francs.