John Stamos is celebrating a new chapter in his son's life.

His son, Billy Stamos, 4, had his first day of school on Wednesday so the actor shared a photo of them to mark the occasion on Instagram.

"One of us is starting his first day at school," Stamos wrote in the caption. "And the other is doing everything in his power not to cry."

The "Full House" star and his wife, Caitlin McHugh, welcomed Billy into the world on April 10, 2018.

Over the years, Stamos has shared sweet moments on social media of his family.

"He's the light of our life," Stamos said about his son in an interview with "Good Morning America" last year.