Have you ever wondered whether there’s something very valuable sitting around your house, and you don’t even know it? A woman in England bought what she thought was a costume jewelry ring 30 years ago, and wore it all the time. It turned out to be a 26-carat diamond, which is expected to sell for up to $454,000 at auction this summer.

The ring’s mistaken identity was because diamond cutters’ priorities have changed over the centuries. The head of the jewelry department at Sotheby’s London, Jessica Wyndham, explained to the BBC that in the 19th century, when this ring was created, diamonds were cut to keep the stone as large as possible, and not to emphasize sparkle and reflect more light.

“With an old style of cutting, an antique cushion shape, the light doesn’t reflect back as much as it would from a modern stone cutting,” she said.

At some point between its original sale and the fateful church “car-boot sale” in the ’80s, the ring’s real identity was forgotten, and the diamond and its setting became dirty. The new owner liked her costume jewelry ring so much that she wore it everywhere, including out shopping and while doing housework.

As the family tells it, a jeweler happened to see the ring and recommended that they take it to Sotheby’s to find out whether it might be worth something. They weren’t even sure it was a real diamond, and were shocked to learn its real value.

The ring is part of a jewelry sale at Sotheby’s in June, and is expected to sell for between $321,550 and $448,770 in US dollars.

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