As a child, John Webber often played with the strange engraved metal cup that was lying around in his grandfather's scrapyard.
Even when he inherited the cup from the old rag-and-bone man, he assumed it was simply another piece of bronze or brass which had escaped the melting pot.
But last year Mr Webber, himself now a 70-year- old grandfather, unpacked it from its box after six decades to discover he had been sitting on a fortune.
Experts say the cup is pure gold and dates back to before the birth of Christ.
Next month, it will go up for auction with an estimate of between ￠G50,000 and ￠G100,000, although Mr Webber says he will not be surprised if it fetches half a million.
When they first saw it, experts were baffled by the piece, unlike any they had seen before.
That was until laboratory analysis of the gold put it in the third or fourth century BC.
Now it is thought the intricate design is the work of craftsmen in the days of the Achaemenid Persian Empire, which spanned three continents until Alexander the Great defeated the forces of its last ruler in 330BC.
Mr Webber said the cup was acquired in the late 1930s or early 1940s by his grandfather William Sparks in Taunton, Somerset.
Before his death in the late 1940s he gave it to his grandson because his own son had already died.
Believing it to be brass or bronze, Mr Webber put the cup, along with other gifts, in a box and forgot about it until last year when he moved house.
Only then did he unwrap the cup from tissue paper and realise the long-forgotten toy of childhood might in fact be gold.
Mr Webber, who lives near Taunton, said: 'My grandfather was originally a proper rag-and-bone ban from Romany stock and lived in a caravan.
He formed a scrap-metal company in the 1930s and made enough to have his own house built.
'I remember when I was a boy playing with all the things he had. As a child I remember the faces on the gold cup used to scare me to death.
'I'm sure a lot of pieces ended up in the melting pot, but not this. My grandfather must have known it was of some value.'
Mr Webber sent the cup to the British Museum where experts recommended he have it tested at a laboratory.
Tests confirmed its age and that it had been crafted from just one piece of gold.
Scientist Peter Northover reported: 'The method of manufacture and the composition of the gold are consistent with Achaemenid gold and goldsmithing.'
The vessel is to be auctioned at Duke's auction house in Dorchester on June 5, along with two other items passed down from Mr Webber's grandfather.
They are a gold spoon valued at ￠G10,000 which might have come from Roman North Africa, and a 'Hellenistic' gold mount with a figure thought to be Ajax, probably from the second century BC and valued at up to ￠G2,000.