She bought it for $15, expected to sell it for $450,000, and instead got $848,000 for a whopping 56,500% return on her original investment. The mystery seller, who snatched up a chunky "costume jewelry" ring at a flea market in London in the 1980s, parted with what turned out to be a 26-carat diamond at a Sotheby's auction on Wednesday, CNN reports. It might have been as good a deal for the anonymous buyer as it was for the seller. A diamond expert says the new owner—who is not a private collector but purchased the diamond for "international trade within the industry," per CNN—is "likely to re-cut it into a modern diamond that will emit even more sparkle and potentially be worth a multiple of today's price."
The expert adds the cushion-cut "Tenner" diamond, which originally came in a dirtied, 19th-century mount, was probably owned by royalty or someone of prodigious wealth because there were few diamonds available in that period. The seller had worn the ring almost daily for three decades before deciding to get it appraised within the last few months, says Sotheby's. Also sold at the auction was a Cartier diamond brooch worn by Margaret Thatcher, including on the day she gave her resignation to the Queen, reports the Telegraph. It fetched $105,000, more than double the estimate. A Sotheby's rep attributed the "strong bidding competition" to "so much interest and attention" in the two items. (Another flea market find: a missing Faberge egg.)