Margot Kidder was found unresponsive on a couch in her Montana house Sunday by a friend who stopped by to help with house cleaning, an official told the Daily News Tuesday.
"It was a friend helping her clean her house. She found Margot on the couch, and she went over to talk to her and found her dead," Bruce Becker, the Park County Attorney, told The News.
He said a physical autopsy was conducted Monday.
"We're awaiting the results. The toxicology takes a couple weeks," he said. "Foul play is not considered involved."
Becker said he'd heard reports Kidder was suffering from the flu shortly before her death but that it was too early to comment on whether that was a factor.
See photos of Margot Kidder:
Kidder, best known for playing a tough-talking Lois Lane in four "Superman" movies opposite Christopher Reeve, died "peacefully in her sleep" on Sunday, her manager Camilla Fluxman Pines said in a statement.
Kidder was 69.
"I can't believe she's gone," actress and "Superman" co-star Valerie Perrine, 74, told The News on Monday.
"She was always happy and smiling," Perrine said of Kidder. "It was so easy working with her. She hit her marks. She knew her dialogue. And she was kind. She was my friend."
Perrine played Lex Luthor's girlfriend and accomplice Eve Teschmacher in the first two movies in the franchise.
She said Kidder and Reeve had "undeniable chemistry" that propelled the movies to blockbuster status.
"I can't say anything more, I'm too upset," Perrine said.
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