The letter was written by King Henry VII to his Lord Chancellor in 1499
A long-lost letter revealing details of the first Englishman to lead an expedition to North America is to be published in a historical journal.
Written by King Henry VII, it suggests that Bristol merchant William Weston sailed to the New World in 1499.
Bristol University's Dr Evan Jones said it was "an exciting find" that gave a glimpse of a previously unknown, but epic achievement.
The letter was found almost 30 years ago, but is only now being made public.
The document gives little detail, but makes a tantalising reference to Weston's voyage.
Writing on 12 March 1499, King Henry VII instructs his Lord Chancellor to suspend an injunction against the merchant because he will shortly "with God's grace, pass and sail for to search and find if he can the new found land".
Dr Jones believes it was probably the earliest attempt by any explorer to find the Northwest Passage - a sea-route around North America.
Weston's trip also came just two years after that of Venetian explorer John Cabot - the man many believe to be the first European to "discover" North America.
"Henry VII's letter is an exciting find because so little is known about the early English voyages of discovery," Dr Jones said.
"We knew that our knowledge of the first English expeditions to the New World was very incomplete, but this is beginning to show just how incomplete it is.
"Up till now, no-one has ever even heard of William Weston, yet this letter reveals him to be the first Englishman to lead an expedition to North America."
It is only through a series of twists and turns that the letter has now come to light.
It was actually discovered in 1981 by archivist Margaret Condon who passed it on to eminent historian Prof David Beers Quinn.
However, he failed to publish it, preferring to wait for another historian, Dr Alwyn Ruddock, to release research she was doing on Cabot first.
This never happened and the letter might have been lost forever had it not been for a bizarre request by Dr Ruddock in her will to destroy all of her research notes.
This piqued the interest of Dr Jones who then set about trying to discover what Dr Ruddock had found out.
Finally, it was while doing this that he came across details of Ms Condon's letter.
Dr Jones' article will appear in the academic journal Historical Research this week.