Researchers at the Mauritshuis museum in The Hague made the discovery while preparing for a new exhibition.
The museum's director, Emilie Gordenker, said curator Ariane van Suchtelen suspected that the painting, "The Mocking of Samson," was an original Steen.
"After further research, restoration and technical examination, we have come to the conclusion that not only is this painting by the master himself, but that it is still in excellent condition," Gordenker said. "It's as if the canvas is fresh out of Jan Steen's studio - thrilling!"
The painting is part of the Royal Museum of Fine Arts collection in the Belgian city of Antwerp. It's to be displayed at an exhibition "Jan Steen's Histories," that starts Feb. 15 at the Mauritshuis.
Unusually for such an old painting - Steen completed it in 1676 - the canvas is still attached to its original wooden strainer with the original nails.
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