A director who worked with Val Kilmer says it's no conspiracy ... Val was the absolute worst person he's ever known.

"Conspiracy" director Adam Marcus unloaded on Val in a series of since-deleted social media posts, according to Entertainment Weekly, calling him a "putz" and saying he had no problem speaking ill of the dead.

Adam said of Val ... "Worst human being I’ve ever known… and that is really saying something."

The director clearly expected some backlash over his comments, saying ... "And to any of you rolling your eyes because of the whole ‘don’t speak ill of the dead bulls***,’ f*** that. [If] this guy did one-tenth of what he did on my set today, he would have been cancelled in a blink."

Val starred as William "Spooky" MacPherson, a disabled Iraq War veteran who travels to Arizona to discover that his friend and his family have vanished, in the 2008 action thriller "Conspiracy."

Adam's comments come a little over a year since Val's death ... as you know, in April 2025 he died of pneumonia.

Despite Val having tons of fans, he didn't exactly have a clean-cut reputation on set ... according to Entertainment Weekly, Joel Schumacher directed Val in 1995's "Batman Forever" and labeled him "childish and impossible" and a "psychologically disturbed human being."

Val addressed the criticism while speaking to Rolling Stone in 2003 and admitted he'd been "careless about how I viewed my business." However, he pushed back ... "But I trust that the truth is the truth and a lie is a lie."