A lost watercolour by one of Britain's greatest landscape artists found "stuck among" a number of other paintings at a country estate could fetch £50,000.
The JMW Turner painting of Hampton Court, Herefordshire, was found at nearby Kinsham Court and thought to have been forgotten about over time.
Minster Auctions, which is selling it, said although there was no signature on it, "the signature is in the style".
Expert James Pearn said he was "pretty surprised" to find the painting.
Another Turner painting of Hampton Court dating back to 1795 is part of the V&A's collection.
Kinsham Court was once owned in the early-1900s by John Stanhope Arkwright, who had also previously owned Hampton Court, which is now a wedding venue.
The painting was discovered at Kinsham by one of his descendants, along with four others, and handed to auctioneers.
"The watercolour was in [a file] together with a number of other things," Mr Pearn, the auction house's specialist picture consultant, said.
He said it was "stuck amongst the middle" of some mid-19th Century watercolours and hunting prints which were "nothing very exciting".
"I have to say, I had a pretty good idea of what it was," he said.
"I did genuinely think it was Turner. I was pretty surprised.
"These things do happen."
He said the painting depicted Hampton Court from a south-east direction across the River Lugg.
'All the more exciting'
Mr Pearn said he expected Turner would only have been about 21 when he painted the work.
The artist entered the Royal Academy drawing schools when he was 14 in 1789 and was exhibiting within a year.
"The signature is in the style," Mr Pearn said, adding: "It's just 'literally in the paint', as they say."
"That of course makes it all the more exciting. He does have quite a lot of distinctive features in this."
The painting, which will be auctioned in March, is expected to reach between £30,000 to £50,000 and attract global interest.