GENEVA—A blue diamond weighing nearly 10 carats has sold at auction in Switzerland for 20.5 million Swiss francs ($26.6 million) including fees. The 9.51-carat “Mellon Blue”—named for the late American arts patron Rachel “Bunny” Mellon—had been expected to fetch $20-$30 million at the Christie’s auction on Tuesday. The house said the stone came in on the estimated range. The final price includes the “buyer’s premium” and other fees. The diamond was previously sold in 2014, the year that Mellon died, for $32.6 million, which was one of the highest prices ever paid for a colored diamond at auction, Christie’s says. […]... Keep on reading: ‘Mellon Blue’ diamond sells for $26.6M at Swiss auction