The most expensive gold coin ever to go under the hammer is to go on display in the City of London.
In 2002, a 1933 Double Eagle $20 coin sold for $7.6m (£4.8m), making it the most expensive gold coin in the world to come to auction.
An example of the coin will be displayed at Goldsmiths' Hall in Foster Lane on Saturday and Sunday.
It is possibly the most valuable ounce of gold in the world, said The London Mint Office.
Nearly half a million of the coins were originally minted in 1933 in the midst of the Great Depression - but only 13 are known to exist today.
It is thought to be the first time that a 1933 Double Eagle has been exhibited in Europe.
Only one coin is legally in private hands - all the other 1933 Double Eagles remain the property of the US government.
The US Secret Service is said to investigate any coins which come to light.
Marc Pachter, of the National Museum of American History, said: "The 1933 Double Eagle is a symbol of a shared struggle in an interdependent global economy, both in the early 20th Century and today.
"We are delighted to make one of the greatest treasures of the Smithsonian available to European audiences as part of this unprecedented tour."
Peter Swanston, chief executive of the London Mint Office, said: "This is an incredibly exciting event.
"As well as being immensely valuable, the 1933 Double Eagle is a truly beautiful coin.
"We are thrilled to bring it to London and I'm sure many people will want to come and see this icon of American history."