The oil triptych, titled The Warsaw Uprising, was traced by staff at the Beskidy Museum of the Bielsko-Żywiec Catholic Diocese in southern Poland, officials said.
The work, whose whereabouts had been unknown for decades, dates from the final months of World War II and is considered one of the few surviving examples of Mehoffer’s late period.
Andrzej Szczerski, director of the National Museum in Kraków, called the discovery "a sensation."
The existence of the triptych was previously known only from references in the memoirs of the artist’s wife, Jadwiga Mehoffer, née Janakowska, but its fate remained unclear.
Szczerski said the central panel depicts fighting in Warsaw's Old Town during the 1944 uprising against Nazi German occupation, while the two side panels contain allegorical and symbolic scenes.
The painting is believed to have been created at Mehoffer’s home at 26 Krupnicza St. in Kraków, in response to accounts by participants in the uprising. The building now houses the Mehoffer Division of the Kraków National Museum.
Mehoffer was a leading figure of the Young Poland movement, which emerged in the 1890s, when culture played a key role in preserving Polish national identity during the country’s partitions by Russia, Austria and Prussia.
He died in 1946, aged 77.
(mk/gs)