The 'Big Bang Theory' star broke the tragic news Saturday, posting two black and white photos of her with her beloved Norman, writing ... "💔 earth shattering deep gut wrenching pain I didn’t know was possible. Norman, you were my entire world for 14 years."

Kaley adds, "Thank you for smiling at me as you left this world, confirming for me once again our language was ours alone. You will always have my heart. 💔"

No word on how exactly her pit bull died, but he was a regular on her IG feed as one of several dogs she appears to own and/or adopts on a semi-regular basis. Kaley has a bunch of photos and videos of her and Norman specifically, where they are often snuggling.

She even made an Instagram page for him at one point, which had thousands of followers. It has since been deactivated.

Kaley rescued Norman when he was around 2, and he had a broken leg at the time ... which she nursed back to full health. She's publicly credited him with inspiring her to be an animal rescuer at large -- KC partnered with Paw Works shortly after taking him in, and she's been deeply involved in rescues, adoptions and fostering in and around L.A. ever since.

Norman's death comes on the heels of another one of Kaley's dogs dying just a few months ago -- a pit bull named Petunia, who she and her husband, Karl, adopted as a senior.

While Kaley's had different dogs under her care at various points over the years, it appears Norman was her rock ... and her day 1, so to speak. So, this one's gotta hurt.