Diane Keaton’s cause of death revealed after shocking passing at age 79

Diane Keaton’s cause of death has been revealed.

The “First Wives Club” actress died of pneumonia at age 79 on Saturday, Oct. 11, The Post can confirm.

“The Keaton family are very grateful for the extraordinary messages of love and support they have received these past few days on behalf of their beloved Diane, who passed away from pneumonia on October 11,” Keaton’s relatives shared to People.

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“She loved her animals and she was steadfast in her support of the unhoused community, so any donations in her memory to a local food bank or an animal shelter would be a wonderful and much appreciated tribute to her,” they added.

After Keaton’s death, a friend of the actress revealed her health had “declined very suddenly” in the final months of her life.

“It was so unexpected,” the friend told People at the time, “especially for someone with such strength and spirit.”

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The pal added that Keaton’s health crisis “was heartbreaking for everyone who loved her.”

“In her final months, she was surrounded only by her closest family, who chose to keep things very private,” the friend added. “Even longtime friends weren’t fully aware of what was happening.”

Another friend of Keaton’s, Grammy and Oscar-winning songwriter Carole Bayer Sager, said Keaton “lost so much weight” before her death.

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“I saw her two or three weeks ago, and she was very thin,” Sager, 81, told People on Sunday. “I was kind of stunned by how much weight she’d lost.”

Meanwhile, one of Keaton’s film executive friends told the outlet that Keaton “was funny right up until the end.”

“She lived exactly how she wanted to, which was on her own terms, surrounded by the people and things she really loved,” the pal stated, adding that Keaton “kept a close circle and she liked it that way” in the final years of her life.

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The “Father of the Bride” actress never disclosed if she was battling any illness. She previously survived two bouts with skin cancer and an eating disorder.

She last posted to her Instagram on April 11, sharing a photo of her golden retriever, Reggie. She had not been seen publicly in six months.

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Many of Keaton’s former co-stars Woody Allen, Kimberly Williams-Paisley, Goldie Hawn, Bette Midler, Jane Fonda, Candice Bergen, Mary Steenburgen, Mandy Moore and Leonardo DiCaprio.

Keaton was never married, but she had two children, daughter Dexter, 29, and son Duke, 25, whom she famously adopted after her 50th birthday.

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“I didn’t think that I was ever going to be prepared to be a mother,” she previously told Ladies’ Home Journal. “Motherhood was not an urge I couldn’t resist. It was more like a thought I’d been thinking for a very long time. So I plunged in.”

At her Hand & Footprint Ceremony in 2022, Keaton said her kids “have no interest in what I do, which I think is very healthy.”

“We live a relatively normal — well, sort of normal — life,” she added.