Woody Allen has paid tribute to Diane Keaton in a heartfelt essay.

On Saturday, it was confirmed the actress had died at the age of 79, sparking a flood of tributes from all over Hollywood. In an essay published by The Free Press, filmmaker Allen touched upon both his personal and professional relationship with the iconic star.

"Unlike anyone the planet has experienced or is unlikely to ever see again, her face and laugh illuminated any space she entered," Allen wrote.

During the piece, the 89-year-old director recalled meeting Keaton for the first time at an audition for his 1969 Broadway play titled Play It Again, Sam.

Allen compared the fresh-faced Keaton to a "gorgeous young" female version of Huckleberry Finn when he first laid eyes on her.

While the pair initially struggled to bond during rehearsals, Allen quickly recognised Keaton's talent and then realised he had romantic feelings for her.

"She was shy, I was shy, and with two shy people things can get pretty dull," Allen admitted, before he revealed sharing a meal together changed everything. "She was so charming, so beautiful, so magical, that I questioned my sanity. I thought: 'Could I be in love so quickly?"

Keaton and Allen collaborated on a series of projects throughout the '70s, including Sleeper, Manhattan and Annie Hall, with Keaton winning an Academy Award for Best Actress for her title role performance.

Allen went on to explain how Keaton remained one of his most important influences in the industry.

He wrote: "As time went on I made movies for an audience of one, Diane Keaton. I never read a single review of my work and cared only what Keaton had to say about it."

Elsewhere in the essay, Allen reflected on the end of his romance with the late actress as he admitted he had no idea why they parted ways.

"This beautiful yokel went on to become an award-winning actress and sophisticated fashion icon," he added. "We had a few great personal years together and finally we both moved on, and why we parted only God and Freud might be able to figure out."

Describing the world as "drearier" without her, Allen revealed Keaton's "great laugh" would continue to echo in his head.