By Debbie Emery - Radar Reporter
Sage was Sylvester Stallone's son from his first marriage to Sasha Czack, and after his parents divorced in 1985, the boy became close to his second step-mom, Jennifer Flavin, with whom Sage's action star dad went on to have three more children with.
Growing up in Hollywood, the dark haired mini-me was often seen at his father's side attending premieres and celebrity events, looking like the spitting image of his famous dad.
Sage made his movie debut starring alongside Sly in Rocky V, where he aptly played the title character's on-screen son, Robert Balboa.
As he grew up Sage began to increasingly look like his father, from his brooding Italian-American good looks to his thick wavy hair, and the pair appeared on screen together again in 1996 thriller Daylight.
A loyal family guy, Sage walked the red carpet carrying little half-sister, Scarlet, when their dad revived his most famous role in 2006 for Rocky Balboa.
Sage's shocking death came out of the blue and has overwhelmed his father with grief, a source told Radar. "He is totally stunned and still in a state of shock."
Stallone's rep, Michelle Bega, released a statement Friday afternoon: "Sylvester Stallone is devastated and grief-stricken over the sudden loss of his son Sage Stallone. 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."