Diane Keaton's family revealed the late actress' cause of death on Wednesday.
"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," her family shared in a statement to People magazine.
The family also added, "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."
The 79-year-old's acting career spanned over six decades across film, television and theater. She was the recipient of one Academy Award, two Golden Globe Awards and one BAFTA Award.
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Keaton was best known for her roles in blockbusters like "The Godfather," "Annie Hall," "The First Wives Club" and "Father of the Bride."
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Keaton was born in Los Angeles in 1946, and she pursued an acting career after graduating from Santa Ana College. She moved to New York City and was cast in the Broadway musical "Hair" in 1968.
The actress made her film debut in the 1970s "Lovers and Other Strangers." She went on to reprise her role as Linda in the 1972 film adaptation of "Play It Again, Sam," after playing the character on Broadway. The movie also starred Woody Allen and marked the beginning of their longtime movie collaboration.
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She made her career breakthrough in 1972 after she starred as Kay Adams Corleone, the wife of Al Pacino's Michael Corleone, in Francis Ford Coppola’s iconic "The Godfather." She reprised her role in the film’s sequels, 1974's Academy Award-winning "The Godfather Part II" and the 1990s "The Godfather Part III."
Keaton won an Academy Award for 1977's "Annie Hall," which she starred in alongside Allen.
She also received Oscar nods for 1981's "Reds," 1996's "Marvin's Room," and 2003's "Something's Gotta Give" with Jack Nicholson.
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Her health "declined very suddenly, which was heartbreaking for everyone who loved her," a source told People, adding that her death "was so unexpected, especially for someone with such strength and spirit."
The source continued, "In her final months, she was surrounded only by her closest family, who chose to keep things very private. Even longtime friends weren’t fully aware of what was happening."
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Fox News Digital has reached out to a rep for Keaton for comment.
Fox News' Sophia Compton and Ashley Hume contributed to this report