Bling, bling ✨ A pink diamond closed at auction for $57.73 million in Hong Kong Friday night, the most expensive diamond per carat ever sold. The 11.15-carat Williamson Pink Star diamond sold at a Sotheby’s auction. The $57.73 million price tag includes the auctioneer’s fees. Without the fees, the raw price of the diamond is $49.9 million, or $4.475 million per carat. It had been estimated to sell at about $21 million.