Jonathan Joss Was Deeply Troubled, His Demons Were His Undoing, Ex-GF Says

Jonathan Joss, the "King of the Hill" voice actor shot and killed Sunday, was a deeply complicated man whose demons helped lead to his tragic fate, his ex-girlfriend tells TMZ.

Brandy Trejo, who dated Joss for 13 years during the height of his career, tells us … Joss was the most "self-destructive person" she ever met … and to her, it seemed like he couldn't stand it when something good happened to him.

What's more ... Brandy says she witnessed him drive his neighbors crazy for years with his outbursts and outlandish behavior ... so when she learned a neighbor allegedly killed him in an argument -- she was not shocked.

As we previously reported ... Sigfredo Ceja Alvarez bailed out of jail on Wednesday, and will be confined to house arrest awaiting trial, after he allegedly fatally shot Joss Sunday evening -- he's been charged with murder. The actor's husband, Tristan Kern de Gonzales, called the shooting a homophobic hate crime ... despite Tristan's statement, San Antonio police declared there's no evidence of a hate crime.

As Brandy explains ... Joss was a loose cannon who liked to make trouble -- obviously not an excuse for killing him! -- and she believes he had undiagnosed mental health issues that he only made worse with drugs and booze.

She wasn't just his girlfriend from 2006 to 2019 ... Brandy tells TMZ she became the actor's unofficial assistant and handler during that period of his career ... and it was up to her to cool him off when he went into a random rage on a set.

Joss was best known for playing John Redcorn on the animated TV sitcom "King of the Hill" ... but he had nearly 50 TV and film credits to his name, including in huge film productions like "True Grit" and "Magnificent Seven." And Brandy tells us ... they were kicked off a number of those sets -- 'cause Joss would start trouble with a star or a director.

Brandy's memories with Joss were not overly positive -- she says he was very emotionally abusive and destroyed her self-worth -- and yet, there were pockets of happiness when he would be a good man and take her on his fun Hollywood adventures.