"Welcome Billy Stamos (named after my father) #NotJustanUncleAnymore #Overjoyed", he wrote on the social media platform.
John Stamos is a first-time father, after wife Caitlin Mchugh gave birth to a baby boy.
"I asked.she said yes!.And we lived happily ever after", the actor posted.
John Stamos and Caitlin McHugh are parents to a new baby boy.
John, 54, first revealed he and wife Caitlin, 32, were expecting their first baby back in December, just two months after their fairy tale engagement at Disneyland.
The caption reads "From now on, the best part of me will always be my wife and son".
The actor was quick to receive messages of congratulations from both his fans and his Full House co-stars.
Stamos, who Wednesday model Caitlin, 31, in February after two-and-a-half years together, had talked of his excitement about becoming a father.
The actor is best known for playing Uncle Jesse - the cool uncle to Bob Saget's character's three kids - on "Full House". They had met filming an episode of Law & Order: SVU in 2011, but only started dating a few years later after reuniting on the set of Fuller House.
"I'll be a fun dad".
He previously said: "It's just taken me a lot longer than I anticipated". Every day I say, 'You're doing so great, you're doing so great'.
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