The 10 x 8in (26 x 22cm) panel was a portrait of Johannes Draconites, who was born as Johannes Drach in c.1494. His academic and theological career took him to many parts of Germany where he published numerous treatises in support of Martin Luther and the Reformation.
The auction house attributed the painting to the circle of Bartholomeus Bruyn the Elder who was born in Wesel in c.1493.
Research by the art historian Ingo Sandner came to the conclusion that the painting was in fact an autograph work by the artist himself. This was based on comparison with other known works by Bruyn, who is represented in museums in London, Paris and Vienna among others.
Of particular interest is a portrait of Draconites in the Museum of Art in Philadelphia, which until now was considered to be the only existing oil portrait of the theologian.
The painting in the auction is now considered to predate this and would appear to be the actual basis for all printed portraits which circulated in the 16th century.
Bidding at the auction on May 9 started at €18,500 and after a short tussle, the hammer fell at €24,000 (£21,050). A German collector, bidding by phone, had the deepest pockets.