The National Museum of Wales is investigating how one of its most important artworks once came to be in the possession of senior Nazi Hermann Goering.

The museum, which owns one of the UK’s most important art collections, is conducting special research into its 16th-century portrait of Welsh noblewoman Catrin of Berain, painted by Flemish artist Adriaen van Cronenburgh.

Details have come to light that in 1939 the portrait was bought by Hitler’s second-in-command via a Dutch art dealer.

Experts at the Welsh museum said “alarms bells began ringing”, after it emerged 12 months ago that Goering’s director of art, Walter Andreas Hofer, acquired the piece.

Hofer was sentenced to 10 years imprisonment by a French military tribunal in 1950 for plundering Jewish-owned artworks for Goering’s personal collection, worth an estimated £120 million.

Oliver Fairclough, keeper of art at the museum, said: “We hadn’t looked further into this picture because we weren’t aware it had been abroad at all. We subsequently came across a reference from our files that this picture was in Goering’s possession.

“Our new information from German archives confirms that it had been in Goering’s collection, that it had been bought for him from art dealer D A Hoogendijk on November 26 1940 for 18,750 Dutch guilders, and that it was returned by the Allies to the Netherlands on December 4 1945.”

It remains unknown whether the portrait was among the thousands of works Hofer placed in Goering’s mansions for safe keeping as Berlin fell to the Allied forces. Most of those works were looted from Jewish owners.

Hofer never served his prison sentence, but remained an art dealer after the war. According to historians, he later married the sister of a Jewish art dealer who he helped escape to Switzerland.