"Happy 5 years to the weirdest person I know!" Cuoco prefaced the post. "I don’t remember a moment before you entered my life.. what a boring life that must have been! I love you @mrtankcook !"
Taking note of the "boring" comment, former "Big Bang Theory" co-star and beau Galecki responded.
"Um," Galecki, 45, succinctly reacted — receiving nearly 8,000 likes in the process.
Cuoco then responded with a simple, "LOL."
The two "Big Bang Theory" co-stars dated each other during the first few seasons of their hit CBS sitcom but then broke up after two years together.
"We dated really early on for almost two years. When we did the pilot, I was crushing so hard on Galecki but he had a girlfriend," Cuoco told Dax Shepard on his podcast, "Armchair Expert" in November.
"We got together and just fell mad for each other for two years, but then we broke up," Cuoco said. "Luckily Johnny and I came out of it so brilliantly and we’re closer today than we ever were."
Galecki told CBS Watch! magazine back in November 2013, "We’re dear friends, still. Kaley’s not just an ex, she’s a part of my life. It was a wonderful relationship, but we never spoke a word about it and never went anywhere together," per Entertainment Tonight.
Now, Cuoco is married to equestrian Cook, who she tied the knot with in 2018, while Galecki recently split from Alaina Meyer after two years. They share a son together.
Fox News’ Jessica Napoli contributed to this report