Andy Garcia has paid a heartfelt tribute to his friend and co-star, Diane Keaton.

On Saturday, a spokesperson confirmed the Oscar-winning actress had died at the age of 79. They declined to share any further details.

Following the sad news, Andy posted a still from their 2018 movie Book Club on Instagram.

In the accompanying caption, the actor described his collaborator as "an American original".

"The magical Diane Keaton has passed. Diane will be deeply missed. She will continue to be an American original. A truly unique and sublime artist. A unicorn of sorts. No one like her," he wrote. "Her light will continue to shine forever. In fact, it will shine even brighter as the years pass. A beacon of spontaneity and originality that we all strive for. I was blessed to be in her light. I will carry it with me forever."

Andy also shared three candid snaps of Diane that he took while they were filming The Godfather Part III in Sicily, Italy back in 1990.

"The magical Diane Keaton has passed. I share with you these pictures I took of her in Sicily during Godfather III. Diane, you will be deeply missed, but your sublime light will shine forever," the 69-year-old added.

In addition, a number of other celebrities have paid tribute to Diane.

Alongside a black-and-white portrait of the artist, Goldie Hawn admitted she wasn't "ready" to lose her The First Wives Club co-star.

"We agreed to grow old together, and one day, maybe live together with all our girlfriends. Well, we never got to live together, but we did grow older together. Who knows... maybe in the next life. Shine your fairy dust up there, girlfriend. I'm going to miss the hell out of you," the actress noted.

Elsewhere, Leonardo DiCaprio recalled working with Diane on the 1996 drama, Marvin's Room.

"Diane Keaton was one of a kind. Brilliant, funny, and unapologetically herself. A legend, and icon, and a truly kind human being. I had the honor of working with her at 18. She will be deeply missed," he commented, adding a dove emoji.

Diane is survived by two adopted children, daughter Dexter, 29, and son Duke, 25.