A multi-million-dollar Rodin bust of Napoleon was discovered hiding in plain sight — inside a New Jersey borough hall, officials said Friday.

The 1908 sculpture by the French artist Auguste Rodin, which art experts lost track of in the 1930s, was found in a corner of Morris County borough hall in Madison, city officials and art experts said.

It had been sitting there for nearly 85 years, Madison Mayor Robert Conley told The Post.

“I’ve held meetings in that room for 6 years. People basically leaned on it — like it was their aunt’s old furniture,” Conley said.

“Later we realized, Oh my God, this is a Rodin!” he said. “We didn’t know how valuable it was.”

The white marble bust — valued at between $4 million to $12 million — was donated to the borough hall by the Philanthropist Geraldine Rockefeller Dodge in 1933, he said.

But there was no official record showing the art was Rodin. It was rumored to be — but nobody bothered to authenticate it until two years ago. Officials kept the astonishing discovery a secret until Wednesday for fear it would be stolen, Conley said.

In 2015, the French Rodin expert, Jérôme Le Blay, traveled to New Jersey to verify the art was legitimate.

“He walked in and said, “There you are! Where have you been?” Conley said.

Le Blay told The Post, “The first pictures that they sent me by email immediately struck me.”

When he visited in person, “The inscription on the side of the marble [confirmed it],” he said.

The sculpture will soon be sent temporarily to the Philadelphia Museum of Art. It will then return to the borough hall, which will get beefed up security to protect it.

“The bust will not be treated like it has been for last 85 years,” Conley said.