(NewsNation) — Oscar-winning director Oliver Stone says actor Val Kilmer was “heroic” in his portrayal of Jim Morrison in the 1991 film “The Doors” and believes the late actor should have received Academy Award recognition for his performance.

“Val worked very hard, and unfortunately, I think it was too early for them to recognize that a music film could be worth an Academy nomination for Val,” Stone told NewsNation, reflecting on Kilmer’s life and career. “I always thought he was robbed.”

Kilmer, who died Tuesday night in Los Angeles at age 65, sang many of Morrison’s lyrics himself in the biopic about the iconic 1960s rock band.

Stone said Kilmer’s vocals were incorporated alongside Morrison’s real voice in what he called “a nice mix.”

The director also commented on Kilmer’s approach to his health struggles.

“It got worse. Val got sicker with time,” Stone said. “He was a Christian Scientist, so he didn’t respond to the cancer in the right way, but he did what he wanted. He was that kind of individualist.”

Kilmer died from pneumonia, according to his daughter, Mercedes Kilmer. The actor had previously battled throat cancer, diagnosed in 2014, which required two tracheotomies.

Beyond his role as Morrison, Kilmer was known for iconic performances in films including “Top Gun,” “Batman Forever,” “Tombstone” and “Heat.” After attending Juilliard as the school’s youngest-ever accepted student at age 17, Kilmer built a versatile career spanning four decades in Hollywood.

“I mourn his death,” Stone told NewsNation.

The Associated Press contributed to this report