John Stamos, Son, Billy, Jimmy Kimmel

ABC / Instagram

Have mercy!

John Stamos and wife Caitlin McHugh's 6-month-old son Billy made his late-night debut on Jimmy Kimmel Live! and what can we say? The kid's a star.

The 55-year-old Fuller House actor was interviewed on the show's Halloween episode, where he and Kimmel dressed up in '70s costumes. McHugh then appeared onstage holding Billy, with the two dressed up like Robin Williams' character Mork from the '70s comedy series Mork & Mindy, and Mindy.

"Just isn't he just the most beautiful baby?" Stamos asked, kissing the child. "I'm so in love."

"Oh my God, I'm gonna keep this kid away from my daughter, that's for sure," Kimmel said, referring to his and wife Molly McNearney's daughter Jane, 4.

This is the cutest baby I've ever seen," Kimmel continued. "You gotta make more of these."

Stamos and wife Caitlyn McHugh have both occasionally shared photos of their son since she gave birth in April. 

Kimmel also has a son named Billy. In 2017, the host made headlines when he announced on his show that McNearney had given birth to the boy, their second child together, and that he underwent emergency heart surgery to treat a congenital defect.

Last month, Kimmel and Stamos bumped into each other at a Children's Hospital Los Angeles fundraising gala, where the TV host jokingly informed the actor that his son was too young to babysit.

"John only has one child so he doesn't know—18-month-old children cannot babysit a six-month-old, no," Kimmel said.

"What about Jane, can she watch him?" Stamos asked.

"Uh, no, she's 4, she's too young to watch. They gotta be at least 14," Kimmel replied.

"You're no good to me," Stamos told him.

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