Certain £2 coins that were released seven years ago may be worth up to £500 - and many are still in circulation.
The Kitchener coin was created in 2014 to commemorate the start of World War 1, but was unknowingly minted with a crucial mistake.
As reported by WalesOnline, on the head side of coin, the text reading 'two pounds' was accidentally not printed.
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As soon as the mistake was caught, an updated coin was minted and entered circulation - but the original coin with the error is now worth considerably more than £2.
Specialists Coin Hunter have stated that 5,720,000 copies of the coin were struck for circulation, and it is now very difficult to find one of the rare misprints.
However, an unknown number are in circulation, and one was sold for hundreds of pounds at auction.
Lord Kitchener, whose face appears on the commemorative coin, was a senior British Army officer, and was commonly found on propaganda posters.
Writing on its Facebook page, Coin Hunter experts said: "Check your coins that feature Lord Kitchener.
"If the heads side does not show 'TWO POUNDS' - you have an error that appears to be very rare."
If you suspect you may have a rare coin, you can ask the Royal Mint to take a look and check if it is real.
Or if you're thinking of bidding on a coin, you should always be wary of fake coins circulating on eBay.
Websites and Facebook groups from change experts like Coin Hunter can help you work out if a coin is the real deal or not.
