Diane Keaton had a complex past with close pal Woody Allen over the years leading up to her death at the age of 79 on October 11. 

The Oscar-winning actress worked on a number of films with the director, including the 1977 movie Annie Hall which earned her an Academy Award for Best Actress. 

Allen has been left 'distraught' over Keaton's passing in California — with the Los Angeles Fire Department responding to a medical call at the late star's home at 8:08 a.m. on Saturday, per TMZ. 

An individual had been transported to a hospital by ambulance, and sources later confirmed the person had been Keaton. 

Allen is said to be 'extremely distraught and surprised and upset' over the shock news of Keaton's death, an insider told People. 

The pair had 'remained friends' after first crossing paths in the late 1960s and having a romantic relationship. 

The source further told the outlet that Allen 'appreciated her very much' and was also not aware of her declining health. 

'Nobody seemed to know. He was surprised,' the insider expressed.

Allen and Keaton first met in 1969 when she auditioned for a role in his Broadway production of Play It Again, Sam. 

She eventually scored a role in the stage production and garnered a Tony Award nomination for Best Featured Actress in a Play. 

The two stars then continued to work together, with the late actress appearing in eight of his movies. 

In 1977, Keaton took on a leading role alongside Allen in his film Annie Hall — which is believed to have been based on their past romantic relationship. 

'It's not true, but there are elements of truth in it,' Keaton said of the speculation during a past interview with the New York Times. 

The pair are believed to have dated before Annie Hall and had also lived together in a penthouse which offered a view of Central Park in NYC. 

In her 2011 memoir, Keaton reflected on their relationship and had written, 'We shared a love of torturing each other with our failures. 

'He could sling out the insults, and so could I... His insights into my character were dead-on and — duh!— hilarious. I had him pegged as a cockroach you couldn't kill.'

Elsewhere in the book, she also penned, 'I miss Woody. He'd cringe if he knew how much I care about him, but I'm smart enough not to broach the subject. 

'I know he's borderline repulsed by the grotesque nature of my affection. What am I supposed to do? I still love him.'

Despite their romantic relationship coming to an end, their close friendship did not. 

Allen and Keaton went on to collaborate on a total of eight films together aside from Annie Hall, such as Love And Death (1975) and Manhattan (1979). 

The Godfather actress had other notable high profile relationships with other celebrities, including Warren Beatty and Al Pacino. 

Allen went on to have a relationship with Mia Farrow - who starred in 13 of his movies. 

In the early 90s, Allen and Farrow were involved in a contentious custody battle and the actress claimed that daughter Dylan had told her in 1992 that he sexually assaulted her — which he denied. 

In 1992, Allen's affair with Mia's adopted daughter Soon-Yi Previn also came to light. 

Allen and Previn eventually married in 1997 and adopted two children together. 

Keaton has often defended and supported Allen amid the sexual abuse allegations against him. 

Back in 2018 amid the #MeToo movement, the late actress shared a tweet where she defended the star. 

She wrote, 'Woody Allen is my friend and I continue to believe him. It might be of interest to take a look at the 60 Minutes interview from 1992 and see what you think.' 

Keaton also linked the interview in the post to her followers where Allen defended himself against the allegations. 

The source also told People on Saturday that Keaton 'didn't believe that any problems [involving the allegations against Allen] overshadowed the important work that he did and the work they did together.' 

The insider added, 'So she always stood by him. He was always grateful for that. So he always felt close.' 

The source also shared that Keaton and Allen 'used to talk on the phone and communicate. Every time she stood up for him, he would reach out to her and text.' 

When Keaton was honored at the 45th Annual AFI Life Achievement Award ceremony in 2017, Allen took to the stage to reflect on their close friendship. 

'The minute I met her, she was a great, great inspiration to me,' the filmmaker stated at the time. 

'Much of what I've accomplished in my life I owe, for sure, to her. Seeing life through her eyes. She really is astonishing. This is a woman who is great at everything she does.' 

Keaton also had positive words towards Allen when she spoke to The Guardian back in 2014 and said, 'He's the strongest person I've met in my life. He's made of steel.

'And talk about a work ethic — he's one of the people that really did teach me that you have to work hard. But he wanted to. He's the most disciplined person I've known, with the exception of my dad.'

The actress had also been asked to offer comment on the sexual abuse allegations against Allen, to which she replied with, 'I have nothing to say about that. Except: I believe my friend.' 

A family spokesperson confirmed Keaton's passing at the age of 79 to People on Saturday. 

A friend close to the star told the outlet, 'She declined very suddenly, which was heartbreaking for everyone who loved her. It was so unexpected, especially for someone with such strength and spirit.' 

They added, '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.' 

Keaton never married but adopted two children in her 50s: daughter Dexter and son Duke.