A Picasso plundered from the University of Pittsburgh in 1961 has sensationally surfaced more than six decades later — and now the Guggenheim has mounted a do-or-die legal battle against a Massachusetts couple to get it back.

The oil-on-canvas painting, titled “Femme dans un fauteuil” (Woman in an armchair), mysteriously vanished in 1961 while on loan from the Solomon R. Guggenheim Foundation, according to multiple media reports, including Artlyst magazine.

Incredibly, in 2023, a researcher at Christie’s auction house evaluating a possible private sale of a 13.5- by 10.5-inch painting for owners Lawrence Jay Handler and Wendy Cohen Handler made a shocking discovery — it was the missing Picasso.

The discovery was reported to the Guggenheim — and all hell broke loose, turning into a tug-of-war between the Handlers and the museum, which formally demanded the couple give it up, according to the lawsuit.

The case of the missing Picasso began on Feb. 6, 1961, when a University of Pittsburgh student reported the heart-stopping heist from the Student Union building, where it was on display with other works and due to be returned to the Guggenheim at the end of the month.

Police and the FBI launched an investigation, a $100 reward was offered and museums across North America were alerted. At the time, the work was estimated to be worth as much as $100,000.

Then — nothing happened. For 62 years, the tiny Picasso seemingly disappeared off the face of the Earth.

After the Christie’s researchers discovery, the Guggenheim officially demanded it back, according to court papers.

The Handlers refused. They’d bought the work in 1999 from Beadleston Fine Art, a Manhattan gallery that closed in 2002, according to court papers.

On Aug. 10, the Guggenheim filed a lawsuit in New York State Supreme court insisting on the painting’s return — plus $3.5 million in damages.

Court papers do not establish that the Handlers knew the painting had been stolen.

But the Guggenhaim says their ownership trail is crystal clear.

Founder Solomon R. Guggenheim bought the masterpiece from London’s Gallery Zwemmer in 1936, and he was recorded as its owner in Christian Zervo’s 1949 Picasso catalog.

A Guggenheim spokesperson told The Post, “We have attempted to settle the matter with the individuals holding the work. The Guggenheim is and always has been the painting’s rightful owner, and we look forward to its recovery.”

Picasso, who died in 1973 at age 91, painted the work while honeymooning in Biarritz, France, with first wife, ballet dancer Olga Khokhlova.

Although it’s estimated worth was $100,000 in1961, it’s likely worth millions today, although the exact amount has not been publicly divulged.

The Handlers and attorneys for both parties did not return The Post’s inquiries.