The discovery of a landscape painting produced by David Hockney when he was visiting Suffolk more than 65 years ago was a "sparkling revelation", a BBC Antiques Roadshow expert said.
The work, a field in pastel colours, was sold by Hockney to a railway signalman near Felixstowe in 1957, and kept by his family.
His grandson took it to the BBC show and it was valued at £20-30,000.
The programme's art expert Rupert Maas said it was an "extraordinary story".
Getty ImagesRupert Mass described David Hockney as "a living national treasure"The painting's owner, who is not being named by the BBC, appeared on the show that was filmed at Belmont House in Kent.
He said his grandfather was working at the "tiny station" of Trimley St Mary in 1957 when he saw two young artists on the platform.
"He noticed their equipment so he invited them into the signal box to have a cup of tea," he said.
"He eventually invited them home for Sunday lunch because they were living in straitened circumstances.
"He said 'oh, bring a painting' and [grandfather] Wallace bought a painting from each of them.
"A year later, he brandished a piece of paper showing one of these guys [Hockney] had won the gold medal from the Royal College of Art.
"It's a Hockney, that's my case."
AFPHockney's 1970s works include Contrejour in the French Style 1974, left, and Mr and Mrs Clark and PercyMr Maas said he had been "initially incredulous", but as he researched the story, he discovered Hockney had been in the area in 1957, with fellow Bradford Art College student, John Loker.
It was a "gradual dawning to a sparkling revelation by England's greatest living painter", he said.
"When he offered him Sunday lunch, it's the most extraordinary story."
He said it was his job to "question everything, and in this case, I was aware if someone was going to fake a Hockney, it wouldn't look like that".
The pair were staying in the area because they admired Suffolk landscape painter John Constable.
"They made a pilgrimage and it turned out to be a wonderful place to paint - hence this meeting with your grandfather, which is quite extraordinary," Mr Maas told the painting's current owner.
"This is not at all what I am used to seeing by David Hockney," he added, describing it as "very rough and ready", with a "wobbly signature".
"I have this idea they only had green and brown with them, because they were broke," he added.
He pointed out the painting had been "roughly sawn to get it into a frame", which the owner said his mother had done to make it fit.
The owner said he believed it was worth £10,000, but Mr Maas valued it at up to three times that.
The BBC has contacted David Hockney for further comment.
David Hockney
PA MediaOne of David Hockney's best known paintings is A Bigger Splash (1967)- Born in Bradford, West Riding of Yorkshire in 1937
- Rose to fame as part of the Pop Art movement in the 1960s
- Best-known work is probably his swimming pool painting A Bigger Splash, created when he was living in California
- Portrait work includes paintings of his parents, and of dancer Wayne Sleep
- Recent work includes his countryside images of his native Yorkshire, painted in the Bridlington area
Source: Tate Kids
In 2016, a Hockney painting from his time in Suffolk was sold for £32,500 by auctioneer Christie's.
It depicted a street in the village of Kirton, about two miles (3.2km) from Trimley St Mary, and was given as as gift to "Mr and Mrs Rowe from Jon [sic] and David", in 1957.
It is understood the couple ran the village shop which is shown in the painting, and Hockney stayed with them before leaving to study at the Royal College of Art.
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