The diamond ring which was bought for £10 has been sold at a Sotheby’s auction for £656,750.
The jewel was purchased 30 years ago at a car boot sale at West Middlesex Hospital in Isleworth, west London. The owner wore the ring for years unaware that it was a 26-carat diamond.
The owner believed it was a piece of costume jewellery due to its “filthy mount.”
It was only when the owner, who does not want to be identified, took it to Sotheby’s that its true worth was realised. The auction house originally valued the ring at £350,000.
Jessica Wyndham, head of Sotheby’s jewellery department, said: “The owner would wear it out shopping, wear it day-to-day. It’s a good looking ring.
“No-one had any idea it had any intrinsic value at all. They enjoyed it all this time.”
Another highlight of the sale was a Cartier diamond brooch worn by Margaret Thatcher on a number of high-profile public occasions, including the day she offered her resignation as Prime Minister to The Queen.
The brooch sold for £81,250, exceeding its £25,000-35,000 estimate. The proceeds of that sale will be donated to the Endeavour fund – a charity that supports the recovery of wounded, injured and sick servicemen and women.
Overall, the auction made sales amounting to £5.2m.