Brie, who has been married to Franco since 2017, announced the sad news in an Instagram post on Wednesday, June 24, alongside a slide show of photos featuring the puss.
"Said goodbye to this perfect angel today," she wrote. "Harry... Harold... Harrison... my sweet boy. My old man."
She added, "You were quite a talker these last couple years. Your favorite place was in my arms. And your tail was wagging till the very end. The sweetest cat that ever lived."
The "GLOW" star and Franco also share a tabby, named Arturo.
Franco previously revealed the couple initially connected over their love for cats.
"She was the only person I could find who was willing to sleep with my two 16-pound cats on top of her every night, so I didn't have many choices for partners," he told "The Ellen DeGeneres Show" in 2018.