RAPAPORT... Tiffany & Co. will offer a necklace featuring an 80-carat diamond, expected to be its most expensive piece ever, at the reopening of its New York Fifth Avenue flagship store next year.The oval-cut, D-color, internally flawless stone, which the jeweler sourced from Botswana and will set in-house in New York, is at the center of the piece, Tiffany said Tuesday. It is also the largest diamond the company has ever offered. Only the 128.54-carat, yellow Tiffany Diamond worn by both Audrey Hepburn and Lady Gaga is larger, and that piece is not for sale.The jewel is a reimagined version of a Tiffany necklace created in 1939 for the World's Fair, which features an aquamarine in place of the diamond. The unveiling of that piece set the stage for the original opening of the flagship store on the corner of 57th Street and Fifth Avenue in 1940."What better way to mark the opening of our transformed Tiffany flagship store in 2022 than to reimagine this incredible necklace from the 1939 World's Fair, one of our most celebrated pieces when we opened our doors...for the first time," said Victoria Reynolds, chief gemologist at Tiffany. Image: The 80-carat diamond and new necklace design (top); the original 1939 version of the necklace (right). (Tiffany & Co.)