LONDON (AP) ― A painting donated to Britain’s National Trust by the estate of a wealthy supporter has been identified as a Rembrandt self-portrait worth 20 million pounds ($30 million), the heritage body said Monday.

The painting was given to the trust in 2010 by the estate of Edna, Lady Samuel of Wych Cross, whose property-developer husband was a major collector of Dutch and Flemish art. It hangs in Buckland Abbey in southwest England, the former home of 16th-century seafarer Francis Drake.

The portrait of the artist wearing a cap with a large white feather was long thought to have been done by one of Rembrandt’s pupils and was credited as in the “style of’’ the 17th-century Dutch master.

But the National Trust said an investigation led by Ernst van de Wetering, the world’s leading Rembrandt expert, had determined it was by Rembrandt himself.

“It’s amazing to think we might’ve had an actual Rembrandt hanging here on the walls at Buckland Abbey for the past couple of years,’’ said Jez McDermott, the National Trust property manager at the house.

“We never dared think it might actually be an original.’’

Van de Wetering, chair of the Rembrandt Research Project, said that researchers in 1968 had concluded the painting ― which features Rembrandt’s signature and is dated 1635, when the artist was 29 ― was likely by a pupil.

“But over the past 45 years we have gathered far more knowledge about Rembrandt’s self-portraits and the fluctuations in his style,’’ he said.

He said the painting’s crude brushwork and painting technique is observed in other paintings from the early stage of Rembrandt’s career.

The painting has been valued at 20 million pounds ― but the trust, whose mandate is to safeguard Britain’s heritage, is not allowed to sell it.