but one costar and friend tells TMZ that's a total crock. Danny Trejo, who was among the star-studded cast of "Heat" with Val, tells TMZ ... Val got a bad rap for being difficult to work with ...

Danny Trejo says Val Kilmer's reputation for being difficult was unfair and that the late actor was professional and generous on set.

Also appearing during the May 23-25 event include Cary Elwes, Giancarlo Esposito, Danny Trejo and actors from “Saved by the ...