Where James A. Stack Sr. acquired it is a mystery that may never be solved - but for more than 70 years, one of the rarest coins in American history sat quietly in his family's collection.

Stack, a prominent New York banker and one of the most discerning coin collectors of the 20th century, began building his collection in the late 1930s with a bold goal: to assemble the most complete and highest-quality cabinet of U.S. coins possible.

He pored over landmark sales, forged relationships with top dealers, and handpicked pieces not just for rarity, but for their pristine condition and impeccable provenance.

By the time of his death in 1951, Stack's holdings spanned everything from early American copper to spectacular gold issues, along with rarities in U.S. paper money, ancient coins, and world currency.

His collection included some of the greatest trophies in American numismatics - an 1802 half dime, an 1894-S dime, an 1838-O half dollar, the 1815 half eagle, and the finest known 1870-S silver dollar.

Even the notorious 1933 double eagle once sat in his albums before being surrendered to the Secret Service, leaving behind only his wry note: 'Secret Service has mine.'

One of his most elusive prizes - an 1804 silver dollar known as the 'King of American Coins' - has remained hidden since the 1940s. Just 16 examples are known to exist, and this one is considered the finest of the so-called 'Class III' type in private hands.

It will be seen publicly for the first time next week at the American Numismatic Association's World's Fair of Money in Oklahoma City before going under the hammer on December 9, where it's expected to fetch up to $5 million.

John Kraljevich, numismatic historian with Stack's Bowers Galleries, which is handling the sale told Daily Mail: 'It certainly has the upshot of making some people who thought they knew everything about everything, or at least everything about this coin, second guess.

'There's always another collection sitting in grandpa's closet. That's why we do what we do - the joy of discovery and the hunt for hidden treasure.'

Despite its date, no silver dollars were actually struck in 1804. 'None of the silver dollars made in 1804 were actually dated 1804,' Kraljevich explains.

'In 1834 they wanted diplomatic gifts for heads of state, so they made new dies and put 1804 on them.'

Those first pieces went to rulers such as the King of Siam and the Sultan of Muscat - instantly making them rarities.

Later, in the late 1860s and early 1870s, Mint employees struck a few more off the books for collectors. This newly surfaced piece is one of those so-called 'Class III' examples.

Where Stack Sr. acquired the coin remains a mystery.

'We have no backstory,' says Kraljevich. 'The collector bought this between the late 1930s and 1951 in New York... where it was sourced before that is anybody's guess.'

Kraljevich believes the coin's pristine state and fresh-to-market appeal could drive bidding sky-high.

'We're thinking probably four to five million... but anything could happen. People love new discoveries and stories of hidden treasure. You get two wealthy individuals who decide they just have to have it, and records will be set.'

To read the complete article, see:
The 'King of American Coins' is found in 'grandpa's closet' after 70 years... and is set to fetch $5million(https://www.dailymail.co.uk/yourmoney/article-14994417/king-american-coins-grandpas-closet-millions-auction.html)