A diamond ring that was thought to be decorative costume jewelry when it was purchased for 10 pounds in the 1980s sold Wednesday for more than 650,000 pounds ($843,000) at auction.

The 26.29-carat cushion-shaped, claw-set diamond ring had been bought from a car boot sale, according to Sotheby's auction house.

The owner asked the auction house to appraise the ring in recent months, and it had been estimated to be worth between 250,000 and 350,000 pounds.

The ring sold for 656,750 pounds, Sotheby's said.