Bette Midler has offered a heartfelt tribute to her First Wives Club costar Diane Keaton following Keaton's death at age 79. "The brilliant, beautiful, extraordinary Diane Keaton has died," Midler, 79, wrote via Instagram on Saturday, October 11. "I cannot tell you how unbearably sad this makes me." Keaton's spokesperson confirmed to People earlier on Saturday that the Academy Award-winning actress had died of undisclosed causes. Her family "asked for privacy" as they grieve.