A rare gold coin dating back to the 15th century and worth £15,000 ($18,000) has been unearthed by an amateur treasure hunter - who thought it was a bottle top.

The prized coin was made during the brief 86-day reign of King Edward V who was murdered in the Tower of London.

Brian Biddle, 64, found the Angel coin using a metal detector in a farmer's field where it had laid undisturbed for 533 years.

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A rare gold coin (pictured) has been unearthed by a heating engineer. Experts identified it as an Angel coin with an image of Archangel Saint Michael slaying a dragon (left) and the legend 'Edward Di Gra' (outer ring of text) which shows it was minted during the reign of Edward V

WHO WAS KING EDWARD V? Following the death of Edward IV, his 12-year-old son, also Edward, was made King. The young monarch's reign only lasted 86 days before he vanished into a dungeon in the Tower of London along with his brother Richard. It is widely believed they were murdered on the orders of their uncle, who then succeeded Edward V as Richard III. Advertisement

The land in Tolpuddle, Dorset, had been repeatedly searched over the years by members of the Stour Valley Search and Recovery Club before Brian turned up with his detector.

The heating engineer realised he was getting warmer in his hunt for a piece of treasure when his device sounded the alarm.

Mr Biddle said: 'At first I thought it was a bottle top as we find a lot of things like that. But once I got it out of the ground I realised it was a gold coin.'

Mr Biddle, from Bournemouth, took his lucky find to the Dorchester Museum.

Experts identified it as an Angel coin with an image of Archangel Saint Michael slaying a dragon and the legend 'Edward Di Gra' which shows it was minted during the reign of Edward V.

Following the death of Edward IV, his 12-year-old son, also Edward (pictured), was made King. Edward V's reign only lasted 86 days before he vanished into a dungeon in the Tower of London along with his brother Richard, where he was likely murdered

Brian Biddle, 64, found the Angel coin using a metal detector in a farmer's field in Tolpuddle, Dorset, where it had laid undisturbed for 533 years

The earliest surviving portrait of Richard III in Leicester Cathedral

Following the death of Edward IV, his 12-year-old son was made King but the young monarch's reign only lasted 86 days before he vanished into a dungeon in the Tower of London along with his brother Richard.

It is widely believed they were murdered on the orders of their uncle, who then succeeded Edward V as Richard III.

Edward V's reign lasted from April 9 to July 4 but the coin was struck under the orders of Lord Hastings, chamberlain of the Royal Household, who was executed on June 13.

Mr Biddle was declared the owner of the coin which is now to be sold this month at auction in London with a pre-sale estimate of £15,000 ($18,400).

Mr Biddle will split the proceeds 50-50 with the farmer who owns the land where the coin was discovered.

Peter Preston-Morley, a coins expert at auctioneers Dix Noonan Webb, said: 'The story of the little princes in the tower, as they have become known, still fascinates us more than 500 years later and arguments over whether or not Richard was responsible for their deaths are still going on.

'This coin is a very fine and extremely rare find. Very few specimens are known to exist.'