A woman based in London has discovered that a ring she bought 30 years ago and believed to be fake is actually an authentic 26.27-carat diamond, according to Aol.

The ring was bought at a car boot sale for the price of €13.50, the woman unaware of the bargain she had made.

The woman has said to have gone on to worn the ring more often than not, even when doing the most "mundane activities".

After having been advised by a jeweller to get the ring valued 30 years later, the woman has discovered that her everyday hand-candy is a 26.27-carat diamond.

The woman has handed the ring over to Sotheby's London to be auctioned next week on June 7 and it is expected to go for up to €408,862.

A representative from Sotheby's London, Jessica Wyndham, said that the ring seems to have been cut in the 19th century: "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. Cutters worked more with the natural shape of the crystal, to conserve as much weight of the crystal rather than make it as brilliant as possible."

The fortunate woman has chosen to remain anonymous.