Story highlights Postcard-sized painting was bought as part of a job lot at auction for $46 (£30)

Art experts say it is a work by English artist John Constable, worth $390,000 (£250,000)

Painting is thought never to have been on public display before

A postcard-sized painting bought as part of a job lot at an auction for $46 (£30) and left hidden away in a drawer for a decade has been identified as work by John Constable worth more than $390,000 (£250,000).

Robin Darvell bought a cardboard box full of items including the small artwork -- which depicts a rural scene of trees, a bright blue sky and a meadow -- at a sale in Canterbury, southern England more than 10 years ago.

Only a faint signature on the back of its gold frame hinted at its origin. But when Darvell passed the painting on to his son Robert, Darvell junior decided to look into the painting's story, and find out who painted it.

Robert Darvell, 45, director of a film marketing company contacted fakes and forgeries expert Curtis Dowling from British TV show ' Treasure Detectives ' who embarked on a year-long journey, analyzing the paint, canvas and signature to help solve the mystery.

"It's a bit of a dream come true," said Robert. "I was over the moon but also shocked when I found out what the painting really is. It hasn't really sunk in yet.

"It has an emotional value for me. I'm holding something in my hands that Constable painted," Darvell said.

"He's a very lucky man," said art expert Dowling. "Most people assume it's too good to be true."

"When people buy items at auctions that look like they could be worth something, they still wouldn't think they're walking away with a fortune."

Darvell and Dowling believe Constable painted the work as a gift for his father-in-law. It is thought never to have been on public display before.

"Rob certainly didn't expect a miracle," said Dowling. "There are so many convincing forged paintings out there that people would first assume it is fake. Such paintings get lost for many reasons and mostly it looks like something but isn't in the end."

The painting is now tucked away in a bank vault for safe-keeping. Darvell hopes to have it restored before talking to museums to put it on display to the public.

John Constable (1776 - 1837) was an English Romantic painter, famous for his landscapes of the English countryside, particularly scenes of his native Suffolk.

Last year, the Constable painting "The Lock" became one of the most expensive British paintings ever sold, fetching £22.4m ($34.8 million) at an auction at Christie's in London.