Sylvester Stallone Makes Rare Comments About Son Sage's Death in “Sly” Documentary

Asked whether the difficult father-son dynamic he and his son portrayed in ‘Rocky V’ is inspired by life, Stallone said, “Unfortunately, yes”

Sylvester Stallone reflects on triumphs and regrets in the documentary Sly. He also broaches a difficult subject: the 2012 death of his son Sage Stallone.

The actor, 77, has rarely commented on the death of Sage, who died at 36 due to coronary artery disease atherosclerosis, which caused a heart attack.

One of the somber sequences in the Thom Zimny-directed Netflix doc shows footage of Sage at 14, when he played Robert, the son of Rocky Balboa, opposite his father in Rocky V.

That 1990 film’s story centered on Rocky’s difficult relationship with his kid, who feels Rocky spends far more time training with boxer Tommy (Tommy Morrison) than with his family including Adrian (Talia Shire).

When asked in Sly whether his own family dynamics informed the writing of that story — much as his real-life experiences informed Rocky, Rambo and more — Stallone answers, “Unfortunately, yes.”

Related: 5 Revelations from Sylvester Stallone’s Netflix Doc Sly: From a Violent Childhood to His Jealous Dad

He adds, “I try to take something that actually is what I wish I had done in real life, but I wasn’t able to do that in reality. And so quite often I would do it theatrically, magically. … A lot of that is true. Unfortunately, you put things before your family. And the repercussions are quite radical and devastating.”

Sage, whom Stallone shared with actress Sasha Czack, was found dead in his Los Angeles home on July 13, 2012.

“Sylvester Stallone is devastated and grief-stricken over the sudden loss of his son,” said a rep for the actor at the time. “His compassion and thoughts are with Sage’s mother, Sasha. Sage was a very talented and wonderful young man. His loss will be felt forever.”

In 1996, Sage told PEOPLE that when Robert yells at Rocky in the film about not being there for him, it wasn’t entirely acting.

“When I was screaming: ‘You never spent time with me! You never spent time with my mother!’ that was true. I was looking into my father’s face and really saying that,” said Sage at the time.

He added that the real-life dynamic with Stallone shifted after art imitated life while filming Rocky V: “I got a lot of things out. We broke into tears a few times. After the film, everything changed. We’d do anything for each other.”

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After playing glimpses of those scenes featuring Sage in Rocky V, Sly then shows footage from the film’s red carpet premiere in 1990. Standing with his son and talking to reporters, Stallone says, “There’s a line in the movie, ‘I’m so glad he’s born because now I can live through your eyes.’ "

“That, I think, is what fathers look to their children for. It’s an extension of, a slice of immortality. As long as he’s alive, your memory will always be alive, that you did something right. I mean, you hope for that.”

Related: Sylvester Stallone's 5 Kids: Everything to Know

Stallone is also dad to daughters Sophia, 27, Sistine, 25, and Scarlet, 21 whom he shares with Jennifer Flavin, his wife since 1997.

The Expendables actor and Czack also had another son, Seargeoh, now 44. Following Seargeoh’s autism diagnosis, Stallone established a research fund administered under the National Society for Children and Adults With Autism. Speaking to PEOPLE in a 1985 cover story, Stallone said that "Sasha does the hard, in-the-trenches warfare… I use my films to have premieres that raise money for the fund."

Sly is now streaming on Netflix.

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