(CNN) - Uncle Jesse is now a first-time dad.
John Stamos shared a photo late Sunday of his newborn son laying on his chest.
"From now on, the best part of me will always be my wife and my son," Stamos wrote. "Welcome Billy Stamos (named after my father) #NotJustanUncleAnymore #Overjoyed."
Stamos, 54, married actress Caitlin McHugh, 32, in February after popping the question at his beloved Disneyland last October.
Related: John Stamos and Caitlin McHugh get engaged
The couple had announced in December that they were expecting.
"We have the same morals and the same values, that all clicked nicely," Stamos told People at the time. "So we said, 'Oh, well, maybe we should have a family.'"
The "Fuller House" star posted a throwback pic last month from his "Full House" days showing his character, Uncle Jesse, sporting a baby bump and a shirt which read "Bun in the Oven."
"This is the longest 9 months of my life! #cantwait 4 #fatherhood," he wrote in the caption.