A woman purchased a cocktail ring for £10 at a car boot sale in West London in the late 1980s, intending it as everyday jewelry with no idea of its potential value. In 2017, after decades of regular wear, a local jeweller noticed something unusual about the ring and sent it to Sotheby's for evaluation. The Gemological Institute of America confirmed that the ring contained a 26.27 carat cushion cut diamond with a color grade of I and very, very slightly included clarity grade. At auction, this discovery led to the ring being sold for £656,750, making international headlines as one of the most extraordinary finds in recent years.
Written locally by qwen2.5:14b on 2026-10-12,
using this article's own text rather than the other coverage of the
same event (that is the story summary below).
Imagine slipping a cheap, grubby cocktail ring onto your finger, wearing it regularly for many long decades, and never suspecting that it hides a fortune.
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it → imagine → fortune
That is precisely what happened to one woman, who paid just ten pounds for a dull-looking ring at a West London car boot sale, which Americans call a flea market.
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Americans → happen → which
Thirty years later, a local jeweller's glance, a detailed laboratory report and a frenzied London bidding room transformed her bargain into a viral story that made international headlines.
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that → transform → headlines
This article explains where the ring came from, what experts discovered, and why such a find is possible.
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find → explain → what
How a £10 bargain at a West London car boot sale in Isleworth led to an unexpected diamond discovery
In the late 1980s, according to Sotheby's, a woman was browsing a car boot sale in Isleworth, West London, when a box of costume jewellery caught her eye.
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box → lead → eye
She was drawn to some bangles, and paid little attention to a cocktail ring holding a single clear stone.
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She → draw → stone
Sigee writes that the ring sat in a rusty old setting and looked dull and filthy, nothing special at all.
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ring → write → setting
The seller wanted twelve pounds for the whole lot, and the buyer haggled the price down to ten pounds.
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buyer → want → pounds
The bangles and the ring went home with her.
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bangles → go → her
The Guardian, reporting through the Press Association, confirms that the ring was bought in the 1980s and that its owner believed it was a decorative costume jewel.
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it → report → 1980s
Why the ring looked worthless for thirty years and how a local jeweller suspected a genuine diamond
For three decades the ring was simply an everyday piece of jewellery.
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ring → look → jewellery
Sotheby's reports that its owner wore it regularly, as anyone might wear a cocktail ring, convinced it could not be worth anything.
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it → report → ring
Only in 2017 did she take it to a local jeweller, who immediately sensed something special.
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who → take → something
He suspected a genuine diamond but found it too large to measure accurately, so she telephoned Sotheby's.
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she → suspect → Sotheby
Jessica Wyndham, Sotheby's Head of High Jewelry in Europe, told Sigee that few people imagine they are carrying a stone of such size, adding that "if you've always believed something isn't valuable, there's little reason to question it."
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something → tell → it
Wyndham also explained that the mount, a blend of silver and gold typical of the late nineteenth century, tarnished over time, leaving it darker and duller than modern settings.
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mount → explain → settings
The "Tenner" Diamond (Image: Sotheby's)
What the Gemological Institute of America report revealed about the 26.27 carat cushion cut diamond
Sotheby's sent the piece to the Gemological Institute of America for evaluation, and Sigee reports that the verdict was striking.
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verdict → reveal → evaluation
The cushion-cut diamond weighs 26.27 carats, carries a colour grade of I and earns an impressive clarity grade of very, very slightly included, level two.
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diamond → weigh → grade
The Guardian, in its Press Association report, adds that the stone is thought to have been cut in the nineteenth century, although its history and how it arrived at the Sotheby's sale remain unknown.
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it → add → sale
The older cuts were fashioned to display fire, the splitting of light into spectral colours, whereas modern diamonds are cut to maximise brilliance.
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diamonds → fashion → brilliance
She said these proportions give a distinctive personality that collectors now find especially appealing.
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collectors → say → personality
She added that on first seeing the diamond in person, it was clear the stone was special.
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stone → add → person
How the bidding at the sale pushed the Tenner diamond to £656,750
After the diamond was confirmed as genuine, the story went viral and made international headlines.
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story → push → headlines
The Guardian reports that the sale took place in London and that the stone was snapped up for close to twice that figure, at £656,750, a life-changing sum for its owner according to Sigee.
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stone → report → Sigee
Wyndham said, in comments carried by the Press Association, that it was a thrill to bring the hammer down on two much-discussed objects and see that attention turn into strong bidding competition.
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attention → say → competition
The second object was a Cartier diamond brooch worn by Margaret Thatcher, which achieved £81,250 against an estimate of £25,000 to £35,000, with proceeds going to the Endeavour Fund, a charity supporting wounded, injured and sick servicemen and women.
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proceeds → wear → servicemen
Image: Canva
What the Tenner diamond teaches collectors about checking old jewellery
The story also carries practical lessons.
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story → teach → lessons
Sotheby's has handled jewels found hidden in old curtains, tucked into chair upholstery and uncovered beneath floorboards in forgotten garages, though she stressed that the Tenner diamond is remarkable for its size, quality and extraordinary circumstances.
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diamond → handle → size
For anyone inspired to search a relative's jewellery box, she recommended looking for signatures in the mounts or stamps on the pieces themselves, which are the clearest clues to when an item was made, who made it and its level of quality.
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who → inspire → quality
Sigee adds that every Sotheby's jewellery specialist is a gemologist who can identify the key characteristics of gemstones.
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who → add → gemstones
The diamond's former owner still attends car boot sales regularly, knowing treasures may hide in unlikely places.
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treasures → attend → places
The Aporia
