Photo: All rights reserved.

Johnny Galecki and Alaina Meyer

The Big Bang Theory star Johnny Galecki is a new dad.

The 44-year-old former child star and his longtime girlfriend, Alaina Meyer, 21, have welcomed their son Avery, and the actor took to Instagram on Wednesday to share the happy news.

"With full and grateful hearts we welcome our beautiful son into this incredible world," he captioned a shot of the tot holding his parents' hands. "Thank you for all of your love and support."

The couple revealed the baby would be a boy back in May at a gender reveal party.

Johnny, who previously dated his The Big Bang Theory co-star Kaley Cuoco, and Alaina went public with their romance on social media in September 2018.