Hollywood's finest are mourning Diane Keaton. Fans around the world are coming to grips with the sad news that at 79, the beloved actress has passed away. At this time, details remain slim but a friend told People on Saturday "she declined very suddenly" in recent months, "which was heartbreaking for everyone who loved her." And it's clear she was loved by MANY. In the wake of the devastating news, several celebrities have taken to social media to pay tribute to Diane.