John Stamos and Caitlin McHugh arrive for the 24th Annual Screen Actors Guild Awards at the Shrine Exposition Centre in Los Angeles, California January 21, 2018. The baby boy was named Billy Stamos after the "Fuller House" star's late father.
Stamos, 54, shared the happy news on his Instagram account on Sunday night, posting a sweet photo of his newborn son lying on his chest.
'From now on, the best part of me will always be my wife and my son. "Welcome Billy Stamos (named after my father) #NotJustanUncleAnymore #Overjoyed", he wrote on the social media platform.
John, who was previously married to Rebecca Romijn, admitted a year ago he'd always wanted to be a father and felt it would be a "tragedy" if he never had kids. I just can't. I'm already so emotional and so excited.
Something he has wanted for a long time, and now it is just the right time. "I've had the most lovely blessed life on the planet, and the most honest real thing I could do, I haven't done".
He told Entertainment Tonight: 'I don't know what I would do if I wasn't having a baby right now. Like, I've done everything anyone could ever.
'She is the most graceful person I've ever met in my life, and she's handling pregnancy like a champ.
And the former "E.R". actor previously praised Caitlin - who he married in February - for dealing with her pregnancy "like a champ".
He said: "She's so lovely pregnant". Every day I say, 'You're doing so great, you're doing so great.' Just every day I'm with her I just realize, first of all, how lucky I am, but what a special human she is.
John also insisted he doesn't have any nerves about becoming a dad.