Keanu Reeves has paid a touching tribute to his former co-star, Diane Keaton.

On Saturday, a spokesperson confirmed the Annie Hall actress had died at the age of 79.

They declined to share any further details.

And at the premiere of his new film, Good Fortune, in New York City on Monday night, Keanu reflected on the lasting impact working alongside Diane on the 2003 film, Something's Gotta Give, has had on him.

"Total pro," he told E! News on the red carpet. "She was very nice to me. Generous, generous artist and a very special, unique person."

Keanu went on to reflect on how "cool" it was to watch Diane and fellow actor Jack Nicholson interact on the set of the Nancy Meyers-directed romcom.

"It was cool to be able to see her and Jack Nicholson together," the 61-year-old continued. "Just with the history they shared and the way the fondness and love they had for each other. It's really cool."

In addition, filmmaker Nancy has shared a tribute in memory of her friend of nearly four decades.

"As a movie lover, I'm with you all - we have lost a giant. A brilliant actress who time and again laid herself bare to tell our stories. As a woman, I lost a friend of almost 40 years - at times over those years, she felt like a sister because we shared so many truly memorable experiences," she mused. "As a filmmaker, I've lost a connection with an actress that one can only dream of. She was fearless, she was like nobody ever, she was born to be a movie star, her laugh could make your day and for me, knowing her and working with her - changed my life."

To conclude the emotional post, Nancy added: "Thank you Di. I'll miss you forever."

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