He just turned 1, but Jimmy Kimmel‘s son Billy already has plenty of celebrity fans.
Justin Theroux dedicated a special birthday tribute to the little boy on Instagram over the weekend, posting four adorable photos of himself with Billy. Alongside the images, Theroux wrote a message about his health battles over the past year.
“Happy ONE year birthday Billy! 🎂,” he captioned the snaps. “A boy who in 365 days has done more for American national health care than we could all wish to do in our lifetimes. He doesn’t even know yet how courageous he is. An honor to know him and his incredible and equally courageous parents. ❤”
Theroux finished the message by thanking Cedars-Sinai Hospital and Children’s Hospital Los Angeles and reminding fans “#registertovote.”
Theroux, who recently split from Jennifer Aniston after two years of marriage, wasn’t the only star wishing Billy a happy first birthday. Julia Louis-Dreyfus, Tom Arnold and Ellen DeGeneres also shared in the celebrations.
“Happy birthday to dearest Billy!” wrote the Veep star, while DeGeneres applauded Billy as “one tough kid.”
Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Babies newsletter.
Kimmel and his wife Molly McNearney revealed that their son underwent two heart surgeries after he was born with a congenital heart condition, tetralogy of Fallot with pulmonary atresia. Last May, the two-time Oscars host announced during a tearful address that Billy had open heart surgery at three days old as a result of his son’s “pulmonary valve [being] completely blocked and a hole in the wall between the left and right sides of his heart.”
Billy had a second surgery at the Children’s Hospital Los Angeles in December, seven months after his birth. (Kimmel and McNearney also share 3-year-old daughter, Jane. He also has two older children – Kevin and Katie – from a previous relationship.)
Kimmel used his platform to become an advocate for universal health care coverage, as well as other political issues, including gun violence prevention.
Kimmel celebrated his son’s birthday with a sweet post thanking the medical professionals who helped save Billy’s life.
“A yr ago today, God gave us this tough little boy. Today, we thank the nurses & doctors at @CedarsSinai & @ChildrensLA who saved his life & those who shared thoughts & prayers,” the late night host wrote along with an adorable photo of Billy wearing a birthday hat and red bow tie.
“We cannot stay quiet. Please wish Billy happy birthday by REGISTERING TO VOTE! vote.gov,” the father of four added.
McNearney also shared a shot from the birthday bash, in which she gave the little boy a kiss on the forehead.
“One year ago I pushed this little fighter into the world,” she wrote. “He’s taught me true strength and joy. We promise to keep fighting for kids like you, sweet Billy. Thank you God for this light.”