Three sisters from Ohio are in for a staggering financial surprise after discovering the true value of a coin they inherited from their late brother.

The siblings are now the proud owners of a rare dime (10 US cents), minted by the U.S. Mint in San Francisco in 1975 - a coin which had been locked away in a bank vault for some 40 years.  That year, the mint issued 2.8 million special uncirculated "proof" sets containing six coins, which retailed at $7 each.

It was only years later that collectors realised two dimes from these sets were missing the 'S' mint mark, making them incredibly rare. Ian Russell, president of GreatCollections, has indicated that the sisters' dime could command an eye-watering $500,000 (around £384,000) at auction.

The coin, bearing the image of former US President Franklin D. Roosevelt, is especially valuable because of this omission. The other erroneous dime fetched $456,000 (about £350,000) when it went under the hammer five years ago, before later being sold on again to a private collector. 

"They were hidden for decades," Russell disclosed to the Independent, noting that most major collectors and dealers have never even laid eyes on one. He also shared that the sisters, who wish to remain anonymous, revealed their brother and mother acquired the coin back in 1978 for $18,200 - roughly equivalent to $90,000 (around £69,000) today.

Their family, which ran a dairy farm, viewed the coin as a financial safety net in case of economic hardship in the future. One of the sisters revealed to Russell that their brother often mentioned the coin's existence, yet she never laid eyes on it herself until 2023, following his sudden passing. 

Russell had been privy to the dime's story for years, meanwhile, having been let in on the secret by the brother long before. The heartwarming story captured the hearts of many on YouTube after being shared by content creator Andy Jiang. 

One user commented: "Screw the actual monetary amount it's worth, it's really beautiful it was setup to have them told how much after everyone had passed to let them in on the secret," while another wrote: "RIP to the mum and brother, that's truly a beautiful gesture."

A third user expressed: "It's honestly so sweet because you can see how much their mother and brother loved them." A fourth gushed: "Mum and brother looking out, even from the grave."

Whilst a fifth reflected on the bittersweet tale, penning: "I'm sorry they had to lose their mum and brother to find out about the dime, but what a beautiful thing they did for the family they left behind."