A painting by Austrian artist Gustav Klimt that was believed to be lost for about 100 years has been found – having been secretly owned by a private collector for decades. The painting, which was confiscated by the Nazis, is being auctioned as part of an agreement to turn in art once confiscated by the Nazis, according to auction house im Kinsky.

The Austrian auction house says the unfinished painting "Bildnis Fraeulein Lieser" (Portrait of Miss Lieser) was one of the artist's last works before his death. It is unclear who "Fräulein Lieser" is exactly, but experts believe it could have been one of several women in the Lieser family, a wealthy Jewish family in Vienna who were clients of Klimt. 

The woman in the portrait visited Klimt's studio nine times to pose for him, the auction house said. The finished product is a three-quarter portrait of a woman against a red backdrop, adorned with a cape on her shoulders. 

Klimt started the portrait in 1917 and died of a stroke in February 1918. He left the painting—with small parts unfinished—in his studio and it was given to the Liesers. 

After that, the fate of the painting remained a mystery. A photo of the portrait likely taken in 1925 at an exhibit came with a note: "1925 in possession of Mrs. Lieser, IV, Argentinierstrasse 20." The black-and-white image was the only evidence of the portrait's existence – until now. 

It is unclear what happened to the painting between 1925 and 1960, when the family of the current owner obtained the portrait. The painting was passed down to the current owner through three inheritances.

The auction house called the portrait a "sensation," and said it will be auctioned on April 24. "A painting of such rarity, artistic significance, and value has not been available on the art market in Central Europe for decades," the auction house said.

"Bildnis Fraeulein Lieser" is being auctioned as part of The Washington Principles, a 1998 international agreement that established the procedure for returning art stolen by the Nazis.  

Last year, Klimt's "Dame mit Faecher" (Lady with a Fan) was sold at auction in London for over $100 million, setting a new European art auction record.  

Before the auction of "Bildnis Fraeulein Lieser," the painting will be on display in Switzerland, Germany, Great Britain, Hong Kong and other locations. 

In:
• Austria

Caitlin O'Kane

Caitlin O'Kane is a New York City journalist who works on the CBS News social media team as a senior manager of content and production. She writes about a variety of topics and produces "The Uplift," CBS News' streaming show that focuses on good news.