Pablo Picasso's "Madame Soler."

The German state of Bavaria is refusing to return a $100 million Picasso portrait in its possession that was originally owned by the family of composer Felix Mendelssohn.

The chef d’oeuvre, Madame Soler, had belonged to Paul von Mendelssohn-Bartholdy, from the wealthy family of Jewish financiers and a relative of the 19th-century composer Felix Mendelssohn, but he sold the painting, along with four other paintings by Picasso, in 1934 as the Nazis came to power in Germany.

His heirs are now suing, claiming that Mendelssohn-Bartholdy was forced to sell the valuable art under duress.

The heirs to the Mendelssohn-Bartholdy estate have previously sued both the Museum of Modern Art and the Guggenheim for two Picassos in their possession that had been owned by their ancestor. The family was awarded a $5 million settlement for their efforts.

Madame Soler was sold by the gallery owner who originally purchased the valuable pieces, Justin K. Thannhauser, to the Bavarian State Paintings Collection in 1964.

“This is a case of great historical importance involving Germany’s most famous Jewish family,” the lawyer for the family, John Byrne Jr., told the New York Post.

“We are perplexed and disappointed by Bavaria’s failure to properly address the important issues involved in this matter,” he added.