Got a Carrivagio in Your Closet?

So you're cleaning out the box room one day and you stumble across a box of pictures you haven't seen in a while, a couple old yearbooks, some pants you thought you might be able to fit into again some day, maybe even your old prom dress. But, more likely than not, you're not going to stumble upon a painting that you've thought was a fake all these centuries, and which turns out to be a lost Carrivagio.

Queen Elizabeth did.

She has one of the world's greatest art collections, hundreds of Leonardo drawings, almost 30 Canalettos and paintings by Tintoretto, Vermeer, Holbein and Dürer. In 2006, the Queen acquired her first Caravaggio, worth £50 million or more if she could ever sell it.

The Calling of Saints Peter and Andrew, owned by the Royal Family for almost 400 years, has lain unloved and seldom seen in a storeroom at Hampton Court for decades. Misattributed as a copy of a Caravaggio by an unknown hand, it was valued in thousands rather than millions.

The painting was bought by Charles I in 1637 and after being sold with most of the Royal Collection during the Commonwealth, it was re-acquired by Charles II.

Years of grime, varnishing and zealous over-painting to cover up damage convinced generations of art historians that it was of little merit. It was recently valued at "a few tens of thousands of pounds", mainly because Charles I's stamp was on the back.

The Queen cannot sell the work as she holds the Royal Collection in trust for the nation. But one expert said yesterday that the work, once accepted as genuine, could be worth £50 million or more.

The painting is taken from the scene in St Mark's Gospel where Christ, with Peter and Andrew while they are fishing at the Sea of Galilee, says to them: "Follow me and I will make you become fishers of men." Unusually, Christ is shown without a beard. The Royal Collection has dated it to between 1603 and 1606 when Caravaggio worked in Rome.

A notorious brawler, he fled in 1606 after killing a young man in a fight. He went to Naples and Malta but never returned to the Holy City, dying of a fever in 1610.

A copyist would have almost certainly drawn an outline of the picture he was copying on the canvas but cleaning, X-ray and infra-red investigation of the work revealed none. What they did show were incisions, made for the artist's guidance with the handle of a paintbrush, in the first layer of paint. This was a well-known feature of Caravaggio's technique. The removal of over-painting revealed brushwork that was stylistically consistent with other Caravaggio pictures.

The Queen's thoughts on the discovery are not known.