“SONS OF ANARCHY” star JOHNNY LEWIS once had a promising showbiz career before a catastrophic mental breakdown led to his murderous rampage and his own violent death, stunning Hollywood and making headlines around the world.

In a shocking world exclusive, The ENQUIRER explores a series of journals the troubled actor kept, showing how he turned from “a nice, decent guy” into a “frothing-at-the-mouth” lunatic.

“In his sick mind, the whole world had turned against him,” a source close to Lewis told The ENQUIRER.

The demented star’s festering rage exploded on Sept. 26 when he bludgeoned to death his kindly 81-year-old landlady and ripped apart her beloved cat with his bare hands. Lewis then plunged to death from the roof of his rented Loz Feliz, Calif., home.

The ENQUIRER has uncovered new details about what made him snap, which include his onetime relationship with pop star Katy Perry along with her ex-husband Russell Brand and current boyfriend John Mayer.

We also reveal why Lewis – who once played popular character Half Sack on “Anarchy” — was kicked off the show and turned into what one neighbor called “a ticking time bomb.”

Lewis’ descent into hell is a disturbing but riveting story and, as always, The ENQUIRER has the best coverage around!