Lauren Graham is paying tribute to her Because I Said So costar Diane Keaton following the actress' shocking death. Graham, 58, took to Instagram on Monday, October 13, to share a snippet of a letter Keaton sent her in the years before her passing. "Please don't be a stranger. Please invite me to one of your dinners. And finally .... Please hug yourself in the morning, and remember to write your book, and don't let yourself get anxious, you big winner you. Love, Di," the letter read in part. In the caption of the post, Graham reflected on her meaningful friendship with Keaton over the years, as well as the late actress' massive influence. Diane Keaton's 'The First Wives Club' Costar Goldie Hawn Remembers Actress "A few lines from a letter Diane Keaton wrote me years ago, when writing a book was just a dream of mine," Graham captioned the post. "Her work as an actor was an inspiration to me. Her encouragement changed my life." (Graham is an author many times over, publishing numerous books including 2022's Have I Told You This Already?) Lauren Graham, Diane Keaton. Getty Images (2) Keaton and Graham portrayed mom Daphne Wilder and daughter Maggie, respectively, in 2007's Because I Said So alongside Mandy Moore, Gabriel Macht, Tom Everett Scott, Piper Perabo, Stephen Collins, Colin Ferguson and Tony Hale. In the comments section of Graham's post, fans shared their condolences and memories of Keaton. "This is such a beautiful memory to have ❤️," one person wrote, while another said, "It's the people we meet along the way who help to shape our destiny 🩷." (C)Universal/courtesy Everett Collection "How lucky you are to have this piece of her to treasure for eternity!" a third person wrote, while a fourth person said, "What a precious friend to have. Seems like she was an encourager to all." Keaton's death was confirmed on Saturday, October 11, at age 79. A cause of death was not immediately announced, however, a friend of the star subsequently told People that Keaton's health "declined very suddenly, which was heartbreaking for everyone who loved her." "In her final months, she was surrounded only by her closest family, who chose to keep things very private," the friend told the outlet. "Even longtime friends weren't fully aware of what was happening." Bette Midler Pays Tribute to 'First Wives Club' Costar Diane Keaton Following the news of Keaton's death, Because I Said So's Moore, 41, also shared a tribute for her onscreen mother via Instagram. "They say don't meet your heros but I got to work with one of mine and even call her 'mom' for a few months. An honor of a lifetime," Moore captioned two photos with Keaton via Instagram on Saturday. "What an incandescent human Di is and was. 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." Other stars who got to call Keaton "Mom" onscreen also shared tributes, including Emma Roberts. Roberts, 34, played Keaton's daughter in 2023's Maybe I Do. "The absolute greatest," Roberts wrote via her Instagram Stories along with a photo of Keaton. "So lucky to have worked with her love you Diane."