The Firestarter actor, 35, took to the social media site to share a sweet birthday message to his baby sister, Olivia, who rang in her third birthday on Christmas Day.  “Happy bday lil sis,” he captioned the heartwarming set of photos, which feature the High School Musical alum cradling the little tot. He also included a princess emoji, which appears to be fitting for his baby sis, who was wearing a tiara-like headband in the snaps.  “Pure love in this picture right here ❤️” one of Efron’s followers commented on the post, which has been double tapped by over 3 million fans.   “Well my ovaries are on fire now.. thanks for nothing,” another fan gushed.  “does she need a sister n law” someone else quipped.  Efron’s father, David Efron, welcomed Olivia in 2019. The Greatest Beer Run Ever star also has a brother, Dylan Efron, who commented on the photo, writing, “I think we spoiled her.” Dylan has previously posted photos with Olivia as well, and he even claims to be her favorite of the two brothers.  “My sister turns 3 on xmas day— any gift ideas would be greatly appreciated! Just tryin to stay her favorite brother over here 😁” he wrote in a November post.  “@zacefron you got competition” one user joked in the comments on the post.  “Get her a Zac Efron doll for her birthday ❤️❤️” another person suggested. Not a half bad idea—who wouldn’t want their own Zac Efron doll?