John Stamos Poses with Mini-Me Son Billy for First Day at School Photo: Trying 'Not to Cry'

John Stamos Instagram

John Stamos is celebrating son Billy's milestones!

On Tuesday, the Fuller House star, 59, shared a sweet mini-me moment with his 4-year-old son on Instagram.

"One of us is starting his first day at school. And the other is doing everything in his power not to cry," Stamos wrote alongside a photo of father and son wearing matching white, short-sleeved shirts.

In the pic, Billy stands slightly behind his dad in khaki shorts with shaggy hair and a side-swept part.

Stamos, who shares Billy with wife Caitlin McHugh Stamos, frequently posts about big events and everyday moments with his family.

RELATED: John Stamos Shares Sweet Photos of 'Little Moments' with Son Billy, 4: 'I Like Those the Best'

John Stamos/Instagram

Earlier this week, the trio enjoyed the Spider-Man-themed "Glow Webs Glow" experience at the Santa Monica Pier.

"Wonderful day at "Glow Webs Glow" event celebrating Season 2 of #SpideyandhisAmazingFriends," Stamos captioned a carousel of shots on Instagram, showing the happy family. "I have the honor of playing one of his friends, Iron Man. @disneyjunior #marvel @disneyplus @caitlinskybound."

RELATED: John Stamos Strikes a Superhero Pose with Son Billy During Outing at Disney California Adventure

In June, the actor shared more low-key pictures of him and Billy just hanging out in the backyard.

In the first shot, Stamos sits in a garden while holding Billy on his lap as the two of them laugh together. The dad of one also included a sweet picture kissing his son on the head as the preschooler is wrapped up in a towel.

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"The little moments. The 'micro-transactions' that take place in between life's big events. I like those the best," Stamos captioned the thoughtful post.