Big Bang Theory star expecting first baby and how they reveal the gender is adorable!

Actor Johnny Galecki and his girlfriend are expecting a son. 

The Big Bang Theory star's partner Alaina Meyer, 21, has announced that she and the 43-year-old actor are soon to become parents to baby boy after finding out the sex of their little one at their gender reveal party. 

Alongside a photograph of the happy couple covered in blue paint, Alaina wrote: "To all those who voted boy, you were right!"

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A day I’ll never forget. ❤️❤️❤️ @alainamariemeyer

A post shared by Johnny Galecki (@sanctionedjohnnygalecki) on

Johnny later shared his own photograph from the party of Alaina planting a kiss on his lips and he said it was a day he'll "never forget."

Despite being clearly over the moon at the fact he has a son on the way, Johnny recently said he was secretly hoping that Alaina was carrying a daughter for him. 

Asked if he had painted his nails bright pink as a hint he knows Alaina is carrying a girl, he said two weeks ago on The Talk: "I get a little bored looking exactly the same way for nine and a half months every year playing Leonard.

"So we wrapped and I threw some blue in my hair, then I got superstitious that I was manifesting a boy, when I kind of prefer a girl...Don't play this tape for my child years from now! So, I painted my nails pink to try to even out the energy there."

Johnny and Alaina announced in identical posts shared on Instagram earlier this month that they were expecting a baby together.

They said: "We are absolutely over the moon to announce that we will soon be welcoming a little one into this crazy and wonderful world.

"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."

- Bang! Showbiz