Reese Witherspoon is remembering Diane Keaton, one of her most cherished mentors in Hollywood. While appearing at her company Hello Sunshine's Shine Away event on Oct. 11, the actress, 49, recounted some of her earliest memories of the late Annie Hall star, who died at age 79 in California on Saturday, Oct. 11. "I was 15 years old and I was from Nashville, Tenn., and I didn't know anybody,” Witherspoon said during a discussion with author Harlan Coben about their upcoming novel, Gone Before Goodbye, which took place hours after PEOPLE revealed the news of Keaton's death.