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26.27-Carat 'Tenner' Diamond — Once Thought to Be a Fake — Fetches $849,637 at Sotheby's London

June 13, 2017

The woman who bought a 26.27-carat gem-quality diamond for £10 (about $13) at a car boot sale in London about 30 years ago is now $849,637 richer.

The gem — which has earned the nickname "Tenner" because is was purchased for a 10-pound note — sold for nearly two times the pre-auction estimate after a fierce bidding war at Sotheby's London last week.

The unnamed owner had been convinced the showy ring was a piece of costume jewelry due to its low price, ostentatious center stone and filthy mounting. She cleaned it up and wore it day-to-day, never realizing that the gaudy center stone was actually a VVS2, I-color, cushion-shaped diamond that dated back to the 19th century. Some experts believe that a stone of this size and value might even have royal provenance.

How the ring ended up at a car boot sale — where goods are sold from the boot, or trunk, of a vehicle — may never be known.

What we do know is that the owner, only recently, had been tipped off by a local jeweler that the ring could be very valuable. The owner took the ring to Sotheby’s, which confirmed the authenticity of the diamond with a report from the Gemological Institute of America.

"It was bought as a costume jewel," Jessica Wyndham, head of Sotheby’s London jewelry department, told the BBC. "No one had any idea it had any intrinsic value at all. [She] enjoyed it all this time."

Wyndham explained that the center stone didn't sparkle like a modern-cut diamond.

“With an old style of cutting… the light doesn’t reflect back as much as it would from a modern stone cutting,” Wyndham said. “Cutters worked more with the natural shape of the crystal, to conserve as much weight rather than make it as brilliant as possible.”

Wyndham said the sale of the ring would be life-changing for the owner. She called the ring a “one-off windfall, an amazing find.”

The new owner, who has remained anonymous, is likely to have the Tenner re-cut into a modern diamond, a strategy that will trim its size, while boosting its value.

Credits: Image courtesy of Sotheby’s.