The 43-year-old actor sent love to Helberg, his friend and Big Bang Theory co-star, on the actor's birthday Sunday.
Galecki shared a photo of himself and Helberg attending PaleyFest in March 2016. The picture shows Galecki laughing as he rests his hand on Helberg's knee.
"Happy birthday, Dogbone. Love you, my friend. And promise never to touch your knee again. #simonhelberg," the star captioned the post.
Helberg spent time with Galecki and their co-star Jim Parsons on the Big Bang Theory set Saturday ahead of his birthday.
"My pals," he captioned a photo with the pair.
Galecki, Helberg and Parsons play Leonard, Howard and Sheldon on The Big Bang Theory, which is in its 12th and final season on CBS. Galecki told news.com.au in November the series finale will be emotional.
"The last episode is something that we've talked about for many, many years and there's many variations and options," the actor said.
"I just hope whatever we're doing in that last episode it justifies the characters all crying because I know the cast will be," he added.