Al Pacino reportedly "regrets" not marrying Diane Keaton

Keaton and Pacino - who played a couple, Michael Corleone and Kay Adams-Corleone, respectively, in the films - had an on-and-off relationship from 1971 to 1987 before they split in 1990 because he would not commit to marriage.

A pal of Pacino's told MailOnline: "Looking back, Al admits the love of his life was Diane who he's always called, 'an amazing woman'.

"I know he will forever regret he didn't make his move when he had the chance.

"For years after he and Diane split, Al used to say, 'If it's meant to be, it's never too late for a do-over.'

"But sadly, now it is."

Despite his claimed regret about not asking Keaton for a hand in marriage, the friend says Pacino's children - daughter Julie, 35, who he has with his ex-girlfriend, acting coach Jan Tarrant, 24-year-old twins Anton and Olivia with his ex-partner, 73-year-old actress Beverly D'Angelo, and baby son Roman, two, with his former girlfriend, then-29 year old Noor Alfallah - are the most important people in his life.

The pal added: "Al adores all his kids.

"And although he preferred living in New York, he also purchased a home in Los Angeles just so he could spend more time on the West Coast with his children, who lived there."

Pacino and Keaton lived near each other in Beverly Hills, California, for "years", but they "never" spoke.

The insider continued: "Though he and Diane both lived in Beverly Hills, only a few miles from each other for years, they never spoke.

"I once asked him why, and he told me, 'There's no need to talk with each other. We said everything that needed to be said at the time.'"

Keaton once revealed that she had developed a "crush" on Pacino when they filmed The Godfather in 1971 - in which he played Michael Corleone and she was his second wife, Kay Adams-Corleone.

She once told People: "I was mad for him. Charming, hilarious, a nonstop talker,' she reflected to People years later.

"There was an aspect of him that was like a lost orphan, like this kind of crazy idiot savant. And oh [so] gorgeous."

Keaton - who never married - died on Saturday, and her loved ones have requested privacy as they mourn her loss.

The star is survived by her adopted children, daughter Dexter, 29, and 25-year-old son Duke.