Details surrounding the death are still unknown, but TMZ reports Sage was found in his L.A. home.
Sources told “Extra” that Sage had been going through some personal troubles.
Sage made his film debut at 14, alongside his father in the 1990 movie "Rocky 5" -- playing the role of Rocky's son. He then went on to act in other severalfilms, including the 1996 film "Daylight,” again with his dad.
Sylvester was at Comic-Con 2012 promoting “The Expendables 2." The actor's rep told TMZ, "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."
Sage is the son of Sylvester and Sasha Czack.