The largest in its category, a spectacular blue diamond was auctioned at a total of $23.79 million (17.35 million euros) at a Christie's auction in Geneva.
The sale of the 13.22 carat rock known simply as "The Blue" came on Wednesday, a day after Sotheby's sold a 100-carat flawless yellow diamond for $16.3 million -- with both sales including commission.
When the world's largest orange diamond went under the hammer last November at Christie's in Geneva, it raked in $35.5 million.
The US jeweler Harry Winston bought the blue diamond, described by Christie's as the largest fancy vivid blue diamond in the world, from an anonymous seller.
"Fancy vivid" is the top rating for coloured diamonds.
The company plans to rename the 13.22-carat pear-shaped rock the "Winston Blue".
Harry Winston was bought by watch group Swatch last year.