EXCLUSIVE

The FOX sitcom, "The Mick﻿," was totally nicked from a veteran Hollywood writer who says there's hard proof right in the script ... according to the lawsuit he's filed.

Wyndham Lewis, who's written several seasons of "Nurse Jackie," says he wrote a script in 2015 for a show he called "The Godmother." It was about an irresponsible "black sheep" aunt who suddenly has to care for spoiled rich kids of white-collared criminals. Sound familiar? Yeah, it's the same theme as "The Mick," which stars Kaitlin Olson in the black sheep role.

Lewis says he submitted his script to a FOX exec, named Jen Carreras, but ultimately never struck a deal. Fast forward to January 2016 when -- according to docs obtained by TMZ -- Lewis found out FOX was developing the show he calls a "rewrite" of his 'Godmother' script ... and Carreras was the development exec behind it.

Lewis believes he has a smoking gun, too. According to the suit, the script for a key scene in the FOX show contains a typo, referring to the main character, "Chip" as Grant. He says Grant is the name he gave that character in "The Godmother."

Translation: They changed the names to protect the guilty ... or so he claims.