The legendary actress died last week

Keaton was best known for her roles in The Godfather, First Wives Club and Annie Hall while also collaborating with Woody Allen.

The Hollywood legend won an Oscar for Best Actress in 1977 for her role in Annie Hall.

She also won a BAFTA and a Golden Globe for the same role.

Keaton passed away on October 11, and it caused shockwaves across Hollywood.

She had been out of the public eye for a few months, but no illness had been announced.

A source told People that her health had “declined very suddenly” recently, and that many of her friends “weren’t fully aware of what was happening”.

Her family have now confirmed her cause of death as being pneumonia.

“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 said in a statement to People.

They 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.”

Born in 1946 in Los Angeles, Keaton rose to fame in the 1970s, notably thanks to her role in The Godfather in which she played Kay Adams-Corleone, the second wife of protagonist Michael Corleone.

The Hollywood star got her break in acting with her Broadway debut in the original 1968 production of Hair.

She also starred in a range of much-loved films, including Baby Boom, Interior, Manhattan and Father of the Bride.

Keaton spent three years in a relationship with film maker Woody Allen.

Despite having multiple romantic relationships down the years, Keaton never married.

She told People in 2019: “Today I was thinking, I’m the only one in my generation of actresses who has been a single woman all her life.

“I’m really glad I didn’t get married. I’m an oddball. I remember in high school, this guy came up to me and said, ‘One day you’re going to make a good wife.’ And I thought, ‘I don’t want to be a wife. No.’”

The actress did have two children, a daughter Dexter and a son Duke, whom she adopted in 1996 and 2001 respectively.

Few details have been revealed, but the family have asked for privacy for the time being.

She is survived by her children.