A landscape painting banished to a Norwegian attic after it was decided it was a fake or wrongly attributed has now been identified as a genuine work by Vincent Van Gogh.
It is the first full-size canvas by the Dutch master discovered since 1928.
Sunset at Montmajour depicts twisted holly oaks and a distant ruin bathed in the light of the setting sun, painted with Van Gogh's familiar thick brush strokes.
Experts at the Van Gogh Museum in Amsterdam said the painting was authenticated by letters, style and the physical materials used.
The exact date it was painted can be identified because Vincent described it in a letter to his brother, Theo, and said he painted it the previous day which was July 4, 1888.
He said the painting was done "on a stony heath where small twisted oaks grow."
Museum director Axel Rueger described the discovery as a "once-in-a-lifetime experience" at an unveiling ceremony.
"What makes this even more exceptional is that this is a transition work in his oeuvre, and moreover, a large painting from a period that is considered by many to be the culmination of his artistic achievement, his period in Arles," he said.
The museum as recently as 1991 dismissed the painting as a work by another artist or a fake, in part because it was not signed.
But now the work, belonging to an unidentified private collector, will go on display in Amsterdam from September 24.
New research techniques, including analysis of the pigments in the paint used and their discolouration, used during a two-year investigation convinced experts of its authenticity.
