The birthday girl shared a heartwarming throwback photo of her mom holding her when she was a baby, and wrote in the caption, "Shoutout to my gorgeous mother for cooking me for 9months and welcoming me into the world 28yrs ago today."
"Thank you for showing me what a beautiful, strong, kind, intelligent and magical woman looks like and giving me the best role model a daughter could ask for," Rumer continued. "I love you with all my heart mama. I am so proud to have the honor of being your first baby."
Moore and her then-husband, Bruce Willis, welcomed their first daughter in 1988. The couple, who were married for 13 years between 1987 and 2000, later welcomed daughter Scout in in 1991 and daughter Tallulah in 1994.
Bruce's second wife, Emma Heming Willis, also took to Instagram to send well wishes to her step-daughter on her special day.
Emma shared a heartwarming photo of Rumer holding her infant half-sister Evelyn, which she captioned, "Happy Birthday to the eldest Willis sister… We love you with all our hearts!."
Recently, Rumer sat down with ET where she opened up about her triumphant DWTS victory back in season 20, and talked about returning to the hit ABC series as a guest judge. Check out the birthday girl's exclusive interview below.