The 74-year-old actress Diane Keaton opened up about her brother John Randolph Hall and their relationship, in her new memoir, Brother & Sister. As Diane wrote, her brother got numerous diagnoses over the years, including bipolar disorder and schizoid personality disorder.

Now, at the age of 71, he is suffering from dementia and lives in a care facility. Diane visits him on the weekends.

Diane Keaton opens up about her mentally ill brother in new memoir

Diane Keaton's new memoir also explains her brother John was the inspiration for Annie Hall's "Duane" (Christopher Walken,) the on-screen scary brother of Keaton's character. Woody Allen wanted to depict what Hall's life was like before struggling with dementia: a talented yet disturbed artist.

"Over the years people did a lot of measuring of Randy’s mental status, and it all came to naught. I wanted to explore the mystery of him," said Keaton accordigon to Today, explaining why she decided to write her new memoir.

RELATED: These are the best Woody Allen films

Diane Keaton's brother wasn't able to get professional help when he was younger

John was born two years after Diane. They were really close but she always thought his fears were odd - she wondered why he was always crying and why he was afraid of the outdoors. Then she explained that even though her parents were concerned about her brother's condition, they didn't seek professional help when he was younger - back then, psychological issues were less talked about. 

IN CASE YOU MISSED IT: This is the tragic life of the Little House On the Prairie star Patrick Labyorteaux before being adopted

Diane Keaton regrets about not being around his brother 

Later on, Diane Keaton's brother got help and a psychiatrist began to see him. However, since the actress was busy building up her acting career, she didn't have too much time to spend with him. Now she regrets about not being around and even about how her fame impacted on him. 

RELATED: This is the tragic story of Patrick Swayze's sister Vickie Lynn

John was married for several years but his wife left him. Then he lived alone, drank heavily, and shared with his sister some of his darkest fantasies: "I became addicted to watching horror movies, hoping the films would have some gruesome murder of a woman…" he wrote in a letter to Keaton, which she included in her memoir.

Diane Keaton visits his brother John on Sundays

John Randolph Hall showed first signs of dementia at the age of 65. Before it worsened, he continued making art. He currently lives in a Sunrise senior living facility. Diane visits him on Sundays, and they usually "get vanilla cones and just walk around discovering things."