The 55-year-old actor's baby boy joined his father on Wednesday's episode of Jimmy Kimmel Live, which was a '70s theme in celebration of Halloween. After Stamos and Kimmel briefly talked about how the Fuller House star's wedding was officiated by Beach Boys co-founder Mike Love, it was time to bring out another special guest.
Stamos' wife, Caitlin McHugh, came out holding their son, who was dressed like Robin Williams' TV character, Mork, from the '70s sitcom Mork & Mindy, while his mom was dressed as Mindy.
Needless to say, Billy stole the show. "Isn't he just the most beautiful baby?" Stamos gushed. "I'm so in love."
Kimmel agreed. "This is the cutest baby I've ever seen," he exclaimed. "You gotta make more of these."
Stamos has been busy promoting his new show, You, and was clearly happy to be back with his family in Los Angeles. While on Live With Kelly and Ryan last month, he got emotional talking about being away from his son for so long.
"I miss him! I miss him. This is the longest I've been away from him. I've been waiting my whole life for [fatherhood]," Stamos said while tearing up a bit and grabbing a tissue.
Live wasn't the first time Stamos admitted to missing his son. At the Creative Arts Emmys in September, Stamos and McHugh couldn't stop thinking about their baby boy, telling ET that they just "want to go back home."
"We miss him already," Stamos said. "We just watched a video on the way over here."
McHugh, 32, added, "Even when he’s asleep, I’ll go, like, look at my videos of him because I miss him so much."