Sylvester Stallone was described as "devastated" on Friday after his 36-year-old son Sage, who is also an actor, was found dead.
Sage Moonblood Stallone, who appeared in the 1990s as Rocky Balboa Jr, the son of his father's title character, was found dead at his Hollywood home, media reports said.
"Sylvester Stallone is devastated and grief-stricken over the sudden loss of his son, Sage Stallone. His loss will be felt forever," said a statement issued by his publicist, Michelle Bega.
"His compassion and thoughts are with Sage's mother, Sasha," the statement added, referring to the Rocky star's first wife. "Sage was a very talented and wonderful young man."
The Hollywood A-lister, who is currently promoting his latest movie Expendables 2, was a "wreck," celebrity news website TMZ reported, adding that paramedics were called but Sage was pronounced dead at the scene.
TMZ cited unidentified sources as saying that he had died of an overdose of pills, adding that authorities were trying to establish whether the death was intentional or accidental.
Sage Stallone's attorney George Braunstein said the young actor was not known to be depressed.
"I got a terrible call a few hours ago ... when the housekeeper opened the door and they found what had happened," he told NBC 4 television, adding: "I'm personally devastated. It's just a tragic, tragic loss.
"He was an extremely good actor, a good writer/director, really one of those people who was extremely respectful of Hollywood. He loved his mom and dad. He was a talented, talented person."
He added to the New York Post: "He was in good spirits, and working on all kinds of projects... He was planning on getting married. I am just devastated. He was an extremely wonderful, loving guy. This is a tragedy."
A spokesman for the Los Angeles County Coroner's office, reported to be handling the case, told AFP: "We are in the initial stages of our investigation" but gave no further details.
A spokesman for the LA Police Department (LAPD) said he could not confirm the death, adding: "There's a death investigation, they're waiting for the coroner to identify the body."