Honestly, it still doesn't feel real that we’re talking about Diane Keaton in the past tense. For decades, she was just there—the hats, the gloves, the wide-legged trousers, and that nervous, fluttery energy that made every line feel like she was coming up with it on the spot. But when news broke on October 11, 2025, that the Oscar winner had passed away at 79, the first question everyone had was: wait, what did Diane Keaton die of? She always seemed invincible. Or at least, perpetually youthful in that "quirky aunt who drinks wine and renovates kitchens" sort of way.
The Official Cause of Death
After a few days of speculation and a very private initial grieving period for her family, it was confirmed that Diane Keaton died of pneumonia. Specifically, her death certificate and family statements later clarified it was primary bacterial pneumonia.
It’s one of those things that sounds almost too "normal" for a Hollywood legend, right? But for someone in their late 70s, pneumonia isn't just a bad chest cold. It’s serious. In Keaton’s case, it apparently hit hard and fast. Her family—specifically her children, Dexter and Duke—eventually shared that she passed away in California, surrounded by her inner circle.
A Sudden Decline Nobody Saw Coming
What’s wild is how quiet everything was leading up to it.
Keaton was never one for the paparazzi circuit, but she was usually visible. She’d be posting to her chaotic and wonderful Instagram or getting spotted walking her dogs in Los Angeles. But looking back, there were signs. Neighbors noticed she hadn't been out for her usual walks in the months prior. Even more telling? She put her "dream home" in LA on the market for $29 million back in March 2025.
People who saw her just weeks before she died, like her friend and songwriter Carole Bayer Sager, mentioned she had become very thin.
"I saw her two or three weeks ago, and she was very thin. She had lost so much weight," Sager told People.
It turns out her health had "declined very suddenly." Even some of her longtime friends weren't fully clued in on how bad it had gotten. That was very "Diane," though. She lived her life on her own terms and, apparently, she wanted to leave it that way too—without a public health bulletin or a "brave battle" narrative playing out in the tabloids.
Why Bacterial Pneumonia Is So Dangerous
A lot of fans were confused. How does a woman with that much spark succumb to pneumonia in 2025?
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Medical experts, like Dr. Amanda Overstreet, have since pointed out that bacterial pneumonia (often caused by Streptococcus pneumoniae) can lead to sepsis or respiratory failure extremely quickly in older adults. Even with the best IV antibiotics in a hospital setting, the body's response to the infection can be overwhelming. While we don’t know if Diane had other underlying issues that made her more vulnerable, she had been open in the past about other health battles.
Her History of Health Struggles
Diane wasn't exactly a "private" person about everything. She wrote memoirs. She talked.
She was incredibly candid about two major things that followed her for years:
- Skin Cancer: She dealt with both basal cell and squamous cell carcinoma. It ran in her family (her father and brother had it, too). She famously became a spokesperson for sun safety, which is why you almost always saw her in those iconic wide-brimmed hats and turtlenecks.
- Bulimia: In her memoir Then Again, she revealed she struggled with a massive eating disorder in her 20s. She described eating "buckets of chicken" and whole pies before purging. She eventually credits five-day-a-week therapy for helping her overcome it.
Whether these past struggles played a role in her later health is just guesswork, but they definitely shaped the woman we saw on screen. She was someone who knew what it was like to be "not okay" and turned that into art.
The Legacy Left Behind
Since her passing, the tributes haven't stopped. Emma Stone recently called her a "North Star," and we’ve seen massive retrospectives like the "Looking for Ms. Keaton" series at Film at Lincoln Center.
She didn't leave behind a husband—she famously never married, despite high-profile romances with Woody Allen, Al Pacino, and Warren Beatty—but she left a massive void in the culture. Her final film, Summer Camp, released in 2024, now serves as a bit of a final goodbye to the actress who taught us that you can be a leading lady and a total weirdo at the same time.
If you’re feeling the loss, the best way to honor her isn't just watching Annie Hall for the tenth time (though you should). It’s actually looking at the health lessons she left behind:
- Take respiratory symptoms seriously: If you're over 65 or have a loved one who is, a "nagging cough" or "sudden fatigue" isn't something to ignore.
- Check the vaccines: Bacterial pneumonia is often preventable through the PCV13 or PPSV23 vaccines.
- Wear the hat: Diane was right about the sunblock.
She might be gone, but the "la-di-da" spirit is pretty much immortal.
To keep her memory alive, consider hosting a screening of her "unconventional" hits like Shoot the Moon or Marvin's Room—films that show the depth she had beyond the comedy. Alternatively, you can support the Skin Cancer Foundation, a cause she championed for decades.