Jim Carrey becomes a grandfather!

He may seem a little young to be called "Grandpa," but 47-year-old Jim Carrey is embracing his new role now that daughter Jane Carrey has given birth to a baby boy.

Jane and husband Alex Santana welcomed their first child, son Jackson Riley Santana, at 12:28 a.m. Friday in Los Angeles, PEOPLE confirms. He weighed in at 7 lbs., 11 oz, and measured 20 inches long.

Tweeting about the new arrival, the proud new granddad posted a baby pic and wrote, "Jackson Riley Santana, My Grandson, Born today! This is what 7lbs.11oz. of Calfornia dynomite looks like!"

While she was pregnant, the Jane Carrey Band singer, 22, said she was looking forward to having a son with Santana, lead singer of the metal band Blood Money.

"I'm excited about it because I never really got along with girls growing up," Carrey said last year. "I was a little afraid that if it was a girl that she would not like me, you know? So I'm very happy about the boy."

Her actor dad predicted his little girl would do just fine as a parent.

"Jane is going to be a great mom," he said in July.

Jane's due date was Mar. 3.

By Catherine Donaldson-Evans and Oliver Jones