A drawing bought for just $30 (£22) could be worth as much as $50 million (£37 million).
The drawing in question was purchased by an anonymous bloke in his sixties from a house sale in Concord, Massachusetts, USA, in 2016.
It sat in his house for a couple of years until Clifford Schorer, an American specialist in Old Masters and a senior partner at the London art dealer Agnews, stumbled upon it.
To his astonishment, he believed he could well have been looking at an original by 16th century German Renaissance artist Albrecht Dürer.
Speaking to The Art Newspaper, he said: "It was an incredible moment when I saw the Dürer.
"It was either the greatest forgery I have ever seen - or a masterpiece."
Over the next two years, experts sought to authenticate it, and they did so by establishing that Dürer's 'A.D.' monogram was marked with the same ink as the drawing - which he did with more than 20 other works between 1501 and 1514.
The drawing also featured a trident and ring watermark, seen on more than 200 sheets used by Dürer.
The unknown drawing, which has been titled The Virgin and Child With a Flower on a Grassy Bench (1503), is thought to be a preparatory sketch for The Virgin Among a Multitude of Animals.
The drawing had been in the collection of architect Jean-Paul Carlhian, who died in 2012, followed by his wife Elizabeth three years later.
The family believed the drawing was a 20th century reproduction and the Carlhian daughters jokingly said to the buyer at the house sale: "Oh, so you want the Dürer?"
Schorer negotiated a deal with the buyer prior to it being authenticated and has been given a $100,000 (£75,000) advance, which he has used to pay off his credit cards, re-roof his house, buy a new car and make a generous donation to his church, according to The Times.
The drawing is currently on display at Agnews Gallery in London until 12 December, but the plan is to eventually sell it.
Schorer believes the drawing 'could fetch a record price' of around $50 million - so worth keeping your eyes peeled next time you're down the car booty folks (and learning loads about how to identify works by great German Renaissance artists).
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