For such a work of genius to languish under a false attribution for so long is surely an injustice, but in the end, quality will out

George Gordon, Sotheby's

The work is expected to fetch up to �6m when it goes on sale later this year at Sotheby's.

Old Master paintings specialist George Gordon, who correctly identified the work, said it was discovered after spending years hanging in a religious institution.

"He's an artist of enormous confidence and he's painting a picture of tremendous energy," said Mr Gordon.

'Loaned'

He said Sotheby's alerted after a relative of the owner took a picture of the painting to their offices in Amsterdam.

He said: "The family that owned it never really liked it, they tried to sell it in the 1930s and it was loaned to various institutions.

"But for the last 20 to 30 years it was in the corridor of a religious institution on the continent."

Peter Paul Rubens, a Flemish artist, draughtsman and ambassador, painted the work in Antwerp some time between 1609 and 1611 but it is not known if he was commissioned to do the painting for a wealthy family.

Mr Gordon said the painting heralded a turning point in the artist's life.

"He had just come back from a long stay in Italy, he didn't mature early, he learned his craft very, very slowly through study, and in Italy his reputation grew," he said.

'No hesitation'

"He brought the early baroque style to the north. He's confident and he knows he's a great painter.

"There is no hesitation in the brush strokes and it's not a tentative work."

The painting is due to be sold in July, 22 years to the day after the last Rubens of comparable importance, Sampson and Delilah, was auctioned in 1980 for �2.53m.

Mr Gordon said the painting's excellent condition added to its artistic importance and value.

"This picture will help to illuminate other pictures Rubens painted at the same time," he said.

"For such a work of genius by such a great painter to languish under a false attribution to a minor artist for so long is surely an injustice, but in the end, quality will out."