Karl Cook, a 26-year-old equestrian, shared a funny moment with the 41-year-old actor while visiting Cuoco on the CBS sitcom's set.
"Ummmmmm then this happened @sanctionedjohnnygalecki get off my man! @mrtankcook," the actress captioned a photo on Instagram of Galecki holding and puckering up to Cook.
Cuoco herself cozied up to Cook in another picture she shared with her 3.2 million followers. The equestrian was one of several guests to watch the actress and her co-stars film a new episode.
"Can you tell I [love] when this guy comes to visit me at work?! @mrtankcook," Cuoco wrote.
Cuoco and Cook were first linked in March 2016 following the star's split from husband Ryan Sweeting. She and Galecki, who play Penny and Leonard on The Big Bang Theory, dated in secret from 2008 to 2010.
"We dated, like, five years ago, so I think we've both moved on," the actress said of Galecki in an interview with Watch What Happens Live in 2015.
"Johnny's actually one of my best friends. It's a situation that ended well," she added. "It's been a long time, so it's great. I got lucky."
Cuoco celebrated the Bachelor Season 21 finale with Cook this week during a date night at home. She, Galecki and several other stars will reportedly take a pay cut in future seasons of The Big Bang Theory so Mayim Bialik and Melissa Rauch can receive raises.