Johnny Galecki announced on Instagram Friday that he and his girlfriend Alaina Meyer are expecting their first child.

"Absolutely over the moon to announce that we will soon be welcoming a little one into this crazy and wonderful world," the 43-year-old "The Big Bang Theory" star and "Roseanne" alum captioned a pair of photos of him and Meyer.

"We ask that you please respect our privacy during this celebratory time for us and our families. There truly is love out there for all. We hope ours is the ember of yours, as we feel yours is the ember of ours."

The baby's sex and anticipated birthdate were not immediately revealed. said Galecki and his 21-year-old girlfriend went public with their relationship in September.

Galecki finished work on "The Big Bang Theory" on Tuesday.

He is set to co-host with Kaley Cuoco the send-off special "Unraveling the Mystery: A Big Bang Farewell" on May 16 after their sitcom ends its 12-season run.

Photo credit: Alaina Meyer/Instagram