Sylvester (left) and Sage Stallone, in 1990's Rocky V
07/17/2012 at 07:00 PM EDT
Life was not easy for Sage Moonblood Stallone, particularly as a child, when he had little connection with his busy Hollywood superstar father.
"I was an easygoing guy, and school was pretty much people trying to challenge me to a fight, y'know, saying, 'Rambo! Rocky!' " Sage, who died unexpectedly
last week at age 36, told PEOPLE in 1996, when he was 20.
It galled him because his father, Sylvester Stallone, who had become famous playing a fictional boxer, wasn't often in his son's corner due to his demanding career. So, when Sage got the chance to play opposite his dad as Rocky Balboa Jr. in 1990's Rocky V
, it was a painful as well as cathartic experience.
"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," Sage said. "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."
Sylvester Stallone, 66, was said to be "devastated and grief-stricken" upon learning of the discovery of his son's body last Friday. The cause of Sage's death remains unknown
– and likely will for two months – following an autopsy Sunday.
It was a sad and sudden final chapter to a life that had its ups and downs. In the 1996 interview, Sage told PEOPLE that he became arrogant after his debut on the big screen, and that his father, who was protective, reeled him in.
"To tell you the truth, I was turning into a little spoiled brat after Rocky V
," Sage said. "I was 15 years old, and I thought I was a big shot, like, 'Ay, alright, let's hit the bars, baby.' Trust me, old Daddy put a stop to that real quick."
Sage was always close to his mother, Sasha Czack, the first of Sylvester's three wives. But his reconciliation with his father – they acted together again in 1996's Daylight
– clearly healed some old wounds.
"He'll walk off that set to talk to me now," Sage said at the time. "My father realizes that he did okay with me. He did the best he could."
For more on Sage Stallone's life and unexpected death, pick up the new issue of PEOPLE, on newsstands Friday