One man's trash is another man's treasure, as they say.
And so it turned out for the owner of a diamond ring that they picked up at a car boot sale for £10 30 years ago, which is expected to fetch £350,000 at auction.
They had thought the "exceptionally sized" stone was a piece of costume jewellery when buying it at West Middlesex Hospital, west London, in the 1980s.
However, in actual fact it was a 26 carat, cushion-shaped white diamond from the 19th century. And the owner wore it daily for decades none the wiser. She took it to Sotheby's when a jeweller told her the stone could be valuable.
Now, the stone will be going under the hammer at Sotheby's. The auction house said it will be offered as part of its fine jewels sale on 7 June.
The head of Sotheby's London jewellery department, Jessica Wyndham, said it was bought as a costume jewel so "no one had any idea it had any intrinsic value at all".
"This is a one-off windfall, an amazing find," she added.
The owner had been to a series of car boot sales over the years but didn't have a past of collecting antiques, nor diamonds.
Wyndham said as the older style of diamond cutting was "slightly duller and deeper" than today, it could trick people into thinking it's not a genuine stone.
Still, while that's a diamond find, it's not quite on the scale of a sale earlier this month. A pair of diamond earrings sold for a record-breaking £44m and they didn't even match. The earrings which were different colours, were sold as individual lots, and went for $57.4m (£44.3m) altogether. The flawless 14.5-carat "Apollo Blue" diamond sold for $42.1m, while the 16-carat pink "Artemis Diamond" went under the hammer for $15.3m.