A coin that solved the mystery of a little-known Roman emperor is going on display at a new exhibition.
Mr Malin's discovery is now going on show at the British Museum
The base silver coin, bearing the face of Emperor Domitianus, was found by Brian Malin as he combed a field in Oxfordshire with a metal detector.
Only one other such coin exists, showing the face of the man who ruled Britain for just four days, but was dismissed as a hoax.
Mr Malin's coin is on exhibition at the British Museum in London.
Experts say his discovery proves the earlier coin, found in France 100 years ago, was genuine and that Domitianus did exist.
The coin, estimated to be worth more than £10,000, goes on display on Wednesday at the British Museum in London.
Historians believe Domitianus was briefly the Roman ruler of Britain, an upstart from the legion who was ousted for treason for daring to declare himself emperor and having the coins made.
Mr Malin, a father of one who has been searching for treasure with his metal detector for more than 15 years, found the coin in a field in April last year, 10 miles south-east of Oxford.
It was in a pot of 5,000 others, stuck together and also bearing the heads of emperors.
Dating from 250AD to about 275AD, they spanned five emperors and a time of great upheaval for the Roman Empire.
Domitianus was probably ousted for treason for having the coins made
Richard Abdy, Roman coin curator at the British Museum, said: "The Roman empire was beginning to fray. Domitianus, it looks, ruled in 271AD and there was only one coin with his image.
"There have been references to Domitianus in two ancient texts but they described him as an officer who had been punished for treason."
Dr Chris Howgego, curator for Roman coins at the Ashmolean Museum, said: "It is exciting and valuable and interesting.
"Brian Malin deserves a lot of credit because he did not even delve into the jar and brought it into the museum punctually and he is rather sweet.
"He has not once asked about the value - he has asked 'how important is this and what can we learn?'"
In line with Britain's treasure trove laws, a coroner's inquest will be held and an independent panel will decide how much the 5,000-coin hoard is worth.
The panel will then mediate between the Ashmolean, which has said it wants to buy the pot of coins, and Mr Malin.