Diane Keaton and Al Pacino’s on-off love: The truth about Hollywood's quietest romance

Al Pacino reportedly is having regrets about not marrying Diane Keaton now that the chance is gone.

On Oct. 11, Keaton died at 79. The actress's family told People that they requested privacy and did not share any additional details on her death. 

A close friend of Keaton's told People that her health had rapidly declined prior to her passing. 

"She declined very suddenly, which was heartbreaking for everyone who loved her," a friend of the Oscar winner told People. "It was so unexpected, especially for someone with such strength and spirit."

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"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," the friend added. 

The news of Keaton's death saddened many. Pacino allegedly has been having regrets about not proposing to Keaton after their off-and-on relationship that lasted nearly 20 years. 

"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," a source close to the actor told the Daily Mail.

"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," the source continued. 

Pacino and Keaton were off-and-on from 1971 until they called it quits for good in 1987. The source told the outlet that although they lived minutes from one another in Beverly Hills, they did not stay in communication once their romantic relationship ended.

"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,'" the source said.

Although the pair didn't stay in contact, Pacino honored Keaton at the American Film Institute’s 45th lifetime achievement award in 2017. 

"You’re a great artist. I love you forever," he told Keaton after she received her award, according to Vanity Fair.

Keaton and Pacino's love story began after meeting on the set of "The Godfather," where the actor starred as Michael Corleone and Keaton played his second wife, Kay. 

Their relationship reportedly didn't become romantic until after the movie wrapped filming. In recent years, the two have spoken out about the relationship. 

"I was mad for him. Charming, hilarious, a nonstop talker," Keaton told People in 2017. "There was an aspect of him that was like a lost orphan, like this kind of crazy idiot savant. And oh, gorgeous!"

She told the outlet at the time that she gave Pacino an ultimatum when he wouldn't commit to marriage. "I worked hard on that one. I went about it in not a perfect way," Keaton told People in 2017.

Although Keaton never married, she was involved with other A-list stars, including Woody Allen and Warren Beatty. She adopted her two children, Dexter and Duke, in her 50s and raised them alone.

Keaton had a pretty strong stance on staying unmarried, stemming from a moment in her childhood.

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"I remember one day 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," she told People in 2019.

However, Keaton told The Sunday Times in 2017 that she considered marriage to Pacino.

"I didn’t even want him to propose. I just thought maybe he would marry me, eventually. I thought, ‘don’t even propose — let’s just do it.’ But that never happened, and that is a blessing for both of us. It would have been a nightmare for him."

She continued, "We’re very eccentric, he needed a woman that was going to take care of him, I needed a man who would take care of me … It was just very important that we left each other alone, said goodbye. But it wasn’t my choice."

Pacino never said "I do" either, but fathered four children – Julie Marie, twins Anton and Olivia, and Roman. 

"Al adores all his kids," the source told Daily Mail. "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."

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He mentioned his relationship with Keaton in his memoir, "Sonny Boy." In the book, he wrote about the first time he went broke and Keaton came to his rescue. According to The Guardian, Pacino wrote that following "The Godfather" and "Dog Day Afternoon," he was "spending and not earning; I was putting out but I wasn’t bringing in."

Keaton accompanied Pacino to his lawyer's office and yelled, "Do you know who he is?" 

"You’re going to tell me, ‘Oh, he’s an artist.’ No. He. Is. An idiot. He’s an ignoramus. When it comes to this, you’ve got to take care of him."

Pacino's representative did not respond to Fox News Digital's request for comment.