A Paul Gauguin self-portrait whose authenticity has repeatedly come into question is a true work by the French painter, said its owner, Switzerland’s Kunstmuseum Basel.

The painting, which is commonly thought to be one of the artist’s final ones before his death in 1903, is formally titled Portrait de l’artiste par lui-même and has been held by the Kunstmuseum Basel since 1945.

Even before the painting entered the storied museum’s holdings, however, its authenticity was already being scrutinized. According to the Kunstmuseum Basel, concerns about its attribution were raised as early as 1924, when the painting appeared at auction. When it was shown four years later, in 1928, at the Kunsthalle Basel, it was labeled a “mutmassliches Selbstporträt,” or a “putative self-portrait,” the Kunstmuseum said.

Fabrice Fourmanoir, whom Artnet News once described as an “amateur art sleuth,” resurfaced this debate earlier this year. In an interview with Le Quotidien de l’Art, Fourmanoir claimed that the painting’s true maker was Ky-Dong Nguyen Van Cam, a friend of Gauguin who had produced the work after that artist’s death. The work had already been off view b...