A medal Napoleon gave to British scientist Humphry Davy while France and Britain were at war was thrown away by Davy's widow, a relative has said.
Davy did pioneering work on elements iodine and chlorine
Jane Davy threw her husband's medal into the sea near her Cornish home as it raised bad memories, Margaret Tottle-Smith said.
The couple had made a dangerous voyage to collect the award in 1813, but were mistakenly arrested in Brittany.
The Royal Society of Chemistry has offered over £1,800 for the medal.
It followed the discovery of the letter shedding more light on Napoleon's decision to honour the scientist.
But Ms Tottle-Smith, Davy's fourth great niece, said his widow Jane had thrown it into Cornwall's Mounts Bay.
"It's a very sad story. Humphry married a young widow," she told BBC Radio 4's Today programme.
Jane was very ashamed of the medal and hated it
"She was a socialite - she loved parties, she loved balls and when he died suddenly and the money was cut off, Jane was a widow again with no children.
"She had had a very bad experience going to collect that medal. It was a shocking memory for her.
"A lot of his possessions she gave to the Society because he was president there, but not the medal. I have a feeling that Jane was very ashamed of the medal and hated it."
When she stood at Mounts Bay and threw it off the coast she "got rid of the memories", she added.
The letter - dated March 14 1808, exactly 200 years ago on Friday - was sent by a French navy officer to Jean-Baptiste Delambre, an astronomer and general secretary of the Institut de France.
It said the Emperor's award was intended to "promote and share scientific knowledge" but the British naval blockade prevented news getting through to Mr Davy for years.
In 1813, in the midst of the Napoleonic Wars, he began a voyage across the Channel with Jane and his assistant Michael Faraday in tow.
Davy safety lamps
The RSC believes the three were arrested at Brittany after getting off a ship carrying prisoners-of-war from Plymouth, but were later released.
In Paris they did not meet the Emperor, but met Napoleon's wife Marie Louise instead.
Davy, from Cornwall, was knighted in 1812 and made a baronet in 1818.
He pioneered electrochemistry but is perhaps best known for inventing the Davy safety lamp for miners. He also identified iodine as an element for the first time.