THE "El Dorado of the seas" is one of the world's most valuable shipwrecks with £1billion of gold on board - and it lies somewhere off the UK's coast.
An English galleon named the Merchant Royal sank off Cornwall in 1641.
The 700-ton ship was laden with precious metals, but its wreck has never been found.
Now Cornish treasure hunter Nigel Hodge plans to comb through a 200-square in the English Channel.
He told : "There’s thousands of shipwrecks down there and the Merchant Royal is just one of them.
"We’ve got to literally pick through a lot of wrecks as we’re doing them and then identify them.
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"It’s not straightforward. If it was straightforward, it would have been done."
The Merchant Royal was built at the Royal Naval Dockyard on the Thames in Deptford, south east London and launched in 1627.
Captain John Limbrey and 80 crew sailed the galleon on trading missions around the West Indies, Mexico and Spain.
In 1641 the Spanish treasury hired them to ferry gold and silver to pay 30,000 troops in the Belgian port of Antwerp, which Spain owned.
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The ship picked up the precious metals in Cadiz and set sail - despite springing a leak.
More water seeped on board during a storm, and the ship changed course for England so it could get repaired.
But the Merchant Royal finally sank just 34 miles from Land's End on September 23, 1641.
18 sailors were rescued by another ship, but all of the treasure was lost.
The House of Commons halted proceedings when news of the ship's loss arrived.
King Charles I called the wreckage the "greatest loss ever sustained in one ship".
Described as a broken man, Limbrey lived out his days in Limehouse, east London.
As well as the Spanish gold and silver, the ship carried 400 bars of Mexican silver and 500,000 pieces of eight from its travels.
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The modern-day value of the treasure is often estimated at around £1billion.
In 2019 the search for the shipwreck heated up after a fishing boat named the Spirited Lady netted an anchor thought to belong to it.