A recently rediscovered landscape by British artist John Constable is expected to sell for between £3 million and £5m ($4m-$5.3m) next month.
It sold at auction last year for £40,000 when it was believed to be a copy.
Auction house Sotheby’s said the newly authenticated painting, The Glebe Farm, was an “amazing find”.
There were previously four known versions of the painting by Constable and the work, to be sold on December 8, was thought to be a copy.
"The existence of a lost preparatory study for The Glebe Farm, one of the most personal and evocative of Constable’s great paintings, has long been known by scholars," said Julian Gascoigne, Sotheby’s senior specialist of British paintings.
"Listed in the artist’s studio sale, the re-emergence of this important work after 180 years, particularly in such an exceptional state of preservation, represents one of the most significant and exciting discoveries in Constable scholarship for a generation.”
The Glebe Farm was painted by Constable in memory of friend and mentor John Fisher, who became Bishop of Salisbury. A landscape showing Salisbury Cathedral is another of the artist's most famous works.
Sarah Cove, founder of the Constable Research Project, believes the newly found work was painted by Constable in 1828.
The painting includes a windmill, a subject common in Constable's works, to the right of the farm that is not apparent in the other versions of the work.
Experts also found evidence of rubbing back and toning down of the foliage and foreground details, techniques that were typical of Constable in the 1820s and 1830s.
The Glebe Farm depicts Mr Fisher's parish lodgings when he was Rector of Langham, a small village on the south side of the Stour Valley, Essex, near where Constable was born and grew up in Suffolk.
The painting was in the collection of Edward William Edwards, a US industrialist and art collector, who lived in Cincinnati, Ohio. His family sold it last year.
“The family clearly forgot, or just didn’t realise what they had,” Mr Gascoigne said.
"It’s amazing, really, that in this day and age these things happen and there are still these great masterpieces out there, undiscovered and unknown."
He called the work a “vital link between the various versions of the composition” and “the most significant and important discovery in Constable scholarship for at least a generation”.
Three of the other versions of the painting are at the Tate Gallery in London, with a fourth on display at Detroit Institute of Arts.
The latest version is a "working study" produced by Constable as he moved from the small version of the painting now in Detroit to the larger works at the Tate.
Constable was a Romantic painter most famous for producing landscapes of the English countryside.
His works include The Hay Wain, on display at the National Gallery in London, while another of his paintings, The Lock, sold for £22.8m ($30.5) in 2012.