Sylvester Stallone reflects on his son Sage Stallone's tragic death in his documentary 'Sly.' Here's what happened, and everything Stallone has said.

• Sylvester Stallone reflects on his relationship with his late son in the Netflix documentary, "Sly."

• Sage Stallone, who appeared alongside his father in "Rocky V," died at the age of 36 in 2012.

• Here's everything you need to know about him and the circumstances of his death.

Sylvester Stallone experienced a devastating loss in 2012 when his eldest child, Sage Stallone, died.

Sage, who appeared alongside his father in the 1990 film "Rocky V," was his first child with his first wife, Sasha Czack. The two have another son named Seargeoh Stallone.

Sage was also the half-brother of Sophia, Sistine, and Scarlet Stallone, whom the "Expendables" star, 77, had with his third wife, Jennifer Flavin.

After he made his acting debut at 14 as the titular character's son, Robert Balboa Jr., in the fifth "Rocky" installment, Sage also appeared in the films "The Evil Inside Me," "Vic," and "Daylight," which also starred his father. As an adult, he also worked as a director and executive producer.

He was 36 years old when he died.

How did Sage Stallone die?

Authorities found Sage dead in his home in Studio City, Los Angeles, on July 13, 2012. The New York Post and TMZ, who first reported the news, both speculated that Sage had a prescription-drug problem and died as a result of a pill overdose, citing anonymous sources close to the actor.

Before authorities answered questions about Sage's cause of death, his father made a public appeal for the media to end "speculation and questionable reporting" about his son's cause of death, CNN reported.

"Because when a parent loses a child there is no greater pain," Stallone told the outlet.

"Therefore, I am imploring people to respect my wonderfully talented son's memory and feel compassion for his loving mother, Sasha, because this agonizing loss will be felt for the rest of our lives," he continued. "Sage was our first child and the center of our universe, and I am humbly begging for all to have my son's memory and soul left in peace."

Just over a month after his passing, a spokesperson for the Los Angeles County coroner announced that heart disease from atherosclerosis, not drugs, was Sage's cause of death, CNN reported. The toxicology test showed that Sage had no drugs in his system at the time of his death, except for a small, "sub-therapeutic" level of hydrocodone, commonly sold under the brand name Vicodin, People reported.

Atherosclerosis, which is the build-up of plaque in the arteries, is one of the leading causes of coronary-artery disease, the most common type of heart disease, Insider previously reported.

In July 2012, People interviewed Sage's friends, who told the outlet that he often preferred junk food and cigarettes and was addicted to prescription medication. They also said Sage had a complicated relationship with his father.

During an interview with People published in December 1996, Stallone said his son "avoids the gym like the plague," while Sage added: "People call me a hermit, but I'm happy."

Sage's funeral took place on July 21, 2012, at St. Martin of Tours Catholic Church in Los Angeles, and he is buried at Westwood Village Memorial Park Cemetery, according to The Daily Mail.

What does Sylvester Stallone say about Sage in his Netflix documentary?

"Sly," released Friday on Netflix, reflects on Stallone's life and career in Hollywood.

At one point, he touches upon the parallels between his relationship with his late son and the one between Rocky Balboa and Rocky Jr. as depicted in "Rocky V." In the film, Rocky's mentorship of the boxing prodigy Tommy, played by Tommy Morrison, leaves his son feeling abandoned.

When asked whether he drew from his own experience in writing this storyline, Stallone replied: "Unfortunately, yes."

"You know, unfortunately, you put things before your family, and the repercussions are quite radical and devastating," he added.

Sylvester Stallone says 'Rocky V' was 'too personal'

In the documentary, Stallone described the storyline involving Tommy and Rocky Jr. as being "almost too personal."

Stallone's friend, director John Herzfeld, said that Stallone had his real son cast in the movie to help him break into acting.

"His son, Sage, he put him in it. He wrote him in it. He wanted to give him this opportunity that was so hard for Sly to get," said Herzfeld.

Read the original article on Insider