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Diamond bought for £10 sells for more than £650,000 at Sotheby’s

A diamond ring purchased at a car boot sale for £10 has smashed expectations and sold for £656,750 at auction.

The cushion-shaped diamond, named the ‘Tenner’ diamond, sold for almost double the highest estimated price at Sotheby’s on Wednesday, which had originally predicted the jewel would sell for between £250,000 and £350,000.

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The stone was purchased at a car boot sale in the 1980s at West Middlesex Hospital in Isleworth, west London, under the illusion it was a decorative costume jewel.

The ring was bought under the illusion that it was a decorative costume jewel (Sotheby’s)

However, the ring was recently confirmed by the Gemological Institute of America (GIA) as a genuine diamond from the 19th century weighing in at 26.27 carats.

Speaking to BBC News last month, Jessica Wyndham, head of Sotheby’s London jewellery department, said: “The owner would wear it out shopping, wear it day-to-day. It’s a good looking ring.

“But it was bought as a costume jewel. No-one had any idea it had any intrinsic value at all. They enjoyed it all this time,” she added.

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“They’d been to quite a few car-boot sales over the years. But they don’t have any history of collecting antiques and they don’t have any history of collecting diamonds. This is a one-off windfall, an amazing find.”

Also sold on the day of the auction 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 unique geometric brooch achieved a sale of £81,250 (est. £25,000-35,000), proceeds of which will be donated to the Endeavour fund – a charity that supports the recovery of wounded, injured and sick servicemen and women.

The Cartier diamond brooch worn by Margaret Thatcher on a number of high-profile public occasions (Sotheby’s)