A San Francisco gallery was stunned to discover that it had unknowingly bought a previously-unseen Gustav Klimt drawing.

The Lost Art Salon, which specializes in the rediscovery of fine art, bought a hoard of unidentifiable works on paper at a Bay Area auction last spring. During the research process, gallery staff discovered a series of drawings signed by Johannes and Maria Fischer, who were close friends of Egon Schiele. This clue led the researchers to believe that other pieces could be associated with other Viennese Secessionists.

Eventually the gallery identified a double-sided drawing, bearing the signature of Gustav Klimt’s sister Hermine. She signed several works the artist left behind following his death in 1918. The drawing was subsequently certified as an original Klimt by experts at Vienna’s Albertina Museum.

The drawings portray a seated woman on one side, which bears a close resemblance to Klimt’s Portrait of Sonja Knips (1898), the artist’s first of several commissioned portraits of wealthy Viennese women. The reverse depicts a reclining female nude, which corresponds to the artist’s Fischblut drawing.

Researchers at the Lost Art Salon are still determining the exact provenance details of the unique portfolio. At this point all that is known is that the drawings belonged to a deceased Austrian immigrant who settled in the Bay Area.

The Klimt drawing and a selection of other works from the portfolio will be exhibited at Time Capsule: A Lost Klimt and Other Viennese Treasures which opens at the Lost Art Salon on February 14.