Diane Keaton's famous friends and co-stars have taken to social media to mourn her death at the age of 79. Keaton's The First Wives Club co-star Bette Midler said she was "unbearably sad" at the news in an Instagram post. "The brilliant, beautiful, extraordinary Diane Keaton has died. I cannot tell you how unbearably sad this makes me," Midler wrote. "She was hilarious, a complete original, and completely without guile, or any of the competitiveness one would have expected from such a star." Mandy Moore also reacted to the actor's death, nearly 18 years after they played mother and daughter in Because I Said So. "They say don't meet your heroes but I got to work with one of mine and even call her 'mom' for a few months. An honour of a lifetime," Moore wrote via Instagram. "What an incandescent human Di is and was." She continued, "I am so sad she's gone for all the reasons but also because it felt like she'd be here forever, dazzling us with her talent and charm (and her style, c'mon)! One of the very best to ever do it. All my love to her children and loved ones." Steve Martin marked his Father of the Bride co-star's passing. "Loved!" Martin wrote via X, alongside a black and white throwback photo of a young Keaton. He also shared one of Keaton's famous quotes from her 1977 film Annie Hall: "La dee da, la dee da." Keaton died in California on Saturday. No additional information has been given at this time.