Marcus worked with the late actor - who died in April, 2025 at the age of 65 - on 2008 action thriller Conspiracy in which the actor played an Iraq war veteran who attempts to unravel the mystery behind the disappearance of a friend.
However, the writer/director has now insisted working with the Top Gun star was not a pleasant experience.
In a post on Threads, which has since been deleted, Marcus wrote: "#MicroIntellectMonday to that time when I directed that guy. The guy who played Iceman and Doc Holiday (sic). You know the one.
"Here's me and the Putz working it out on the set of Conspiracy."
Marcus went on to add: "And to any of you rolling your eyes because of the whole 'don't speak ill of the dead bulls***', f*** that. (If Kilmer) did one-tenth of what he did on my set today, he would have been cancelled in a blink."
The moviemaker concluded his post by writing: "Worst human being I've ever known … and that is really saying something."
Kilmer was previously criticised by his Batman Forever director Joel Schumacher in an interview with Entertainment Weekly back in 1996 with the moviemaker branding the actor "childish and impossible" and suggesting he was a "psychologically disturbed human being".
The Island of Dr Moreau director John Frankenheimer also declared he would never work with Kilmer again after they wrapped the 1996 film.
However, Kilmer rebutted both director's comments in a 2003 interview with Rolling Stone, saying: "I've been careless about how I viewed my business.
"But I trust that the truth is the truth and a lie is a lie. Frankenheimer, bless him, he passed on, but he had a history of being mean about people ...
"Schumacher's not a great director by any stretch, but he makes everyone happy, he makes money. But his version of me being unstable - he's very smart, he can't say anything about work, because then I can sue him for slander."
Kilmer also addressed his issues with past work colleagues in his 2021 documentary Val, admitting: "I have behaved poorly. I have behaved bravely. I have behaved bizarrely to some.
"I deny none of this and have no regrets because I have lost and found parts of myself that I never knew existed. And I am blessed."
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