Sage Stallone was 36 years old when he died of a heart attack in 2012.

Sylvester Stallone attends the closing ceremony screening of “The Specials” during the 72nd annual Cannes Film Festival on May 25, 2019 in Cannes, France. (Photo by Gareth Cattermole/Getty Images)

Sage Stallone was the firstborn child of actor Sylvester Stallone and his first wife, Sasha Czack.

Sage was just 36 years old when he died of a heart attack due to atherosclerosis in his Los Angeles apartment on July 13, 2012.

Sage had made his acting debut alongside his father in Rocky V (1990), the fifth installment of the top-rated Rocky franchise. He played Robert Balboa Jr., the onscreen son of his father’s protagonist.

Sage’s parents divorced in 1985, and life wasn’t easy for him when he was younger. “Growing up, my father wasn’t around a lot,” Sage admitted in 1996.

“In school, I would get a lot of hassle because of who he was.”

But the two got closer when they worked together on film. “Sage [and I] are entirely different,” Sylvester Stallone told PEOPLE in 1996.

“He avoids the gym like the plague and is interested in abstract, art-house films.

He has put himself in a position in which he’ll never have to be compared to me … I’m very proud and optimistic.”

Sage’s death shocked his family, and his devastated father begged for solitude and privacy while he grieved the death of his son.

At the time, there were speculations about the cause of death to be related to drugs.

However, a coroner concluded that the 36-year-old had died of heart attack, not drugs, reports CNN.

Stallone appealed to the public to end “speculation and questionable reporting” about his son using drugs.

“Because when a parent loses a child, there is no greater pain,” Stallone said in an emotional statement.

“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. 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.”

At the time, Sage was engaged to be married and was working on several film projects.

He had previously acted in a number of movies as well, including Daylight.

“It’s very, very tough. It’s a horrible situation, but time hopefully will heal, and you try to get through it, but it’s just something that’s a reality of life,” said Stallone.

The action star continued, “It’s important to get back and try to start reliving your life, otherwise you can go into a spiral,” reported The Hollywood Reporter.