Chuck Lorre says his gut instinct to not cast Anna Faris in "Mom" was ultimately proven right ... based on how the show turned out.

The famed showrunner reveals in his new memoir, "Sitcom," that he had "initial reluctance" about putting Anna in the show's starring role.

Chuck writes ... "I initially said no. I wasn't sure Anna would be appropriate for this kind of material."

But Chuck says the way he "bungled" his relationship with Charlie Sheen caused him to reconsider, writing ... "Someone's personal life is none of my business. The mom in 'Mom' would be, and should be, Anna Faris."

When Anna left the sitcom in 2020, Chuck realized he was right all along, explaining ... "As the years went by, it became apparent that my initial reluctance to hire Anna was, in fact, correct."

Chuck says the "mysterious reasons" why Anna left the series after Season 7 "were not mysterious to anyone on the show."

He doubles down ... saying the show "found its true voice" towards the end -- even though it only continued for one more season without Anna before wrapping.