The 36-year-old son of Sylvester Stallone was found dead in his Los Angeles home on Friday, leaving the actor grief-stricken as authorities investigated the cause.
Sage Stallone was found unresponsive by his housekeeper and a relative. There were no signs of foul play or trauma, and no suicide note was found, the city's assistant chief coroner, Ed Winter, said. "Sylvester Stallone is devastated over the sudden loss of his son," publicist Michelle Bega said in a statement. "His compassion and thoughts are with Sage's mother, Sasha."
Sage Stallone was found on Friday afternoon at his home on Mulholland Drive in the Studio City area. On arrival, police confirmed he was dead.
Prescription bottles were recovered in the investigation, but the coroner's office could not say what kind or how many, and whether they had a role in his death. An autopsy will be performed in the next few days and investigators will look into Mr Stallone's medical history, but toxicology tests to establish a cause of death are likely to take several weeks.
George Braunstein, an attorney who has represented Sage Stallone for 15 years, said friends and acquaintances had become concerned because they hadn't heard from him in the past day.
Sylvester Stallone appeared on Thursday at Comic-Con, the San Diego pop culture festival, to promote his forthcoming film Expendables 2 with his friend and co-star Arnold Schwarzenegger. It was not clear whether he had remained at the convention or had returned to Los Angeles on Friday.
Sage Moonblood Stallone was the oldest of Sylvester Stallone's children and co-starred with his father in two films. He was the first of two sons the film star had with his first wife, Sasha Czack, whom he divorced in 1985 after about 10 years of marriage. He has three other children by his third and current wife, Jennifer Flavin. "Sage was a very talented and wonderful young man; his loss will be felt for ever," Mr Bega said.
Sage Stallone made his acting debut in 1990, playing the title character's son, Rocky Balboa Jnr, in Rocky V. He also appeared in the 1996 disaster movie Daylight, in which Sylvester Stallone starred as a hero leading an escape from a collapsed tunnel in New York and his son played a prison inmate.
The same year, Sage Stallone and the veteran film editor Bob Murawski co-founded Grindhouse Releasing, a company dedicated to preserving and promoting the B-movies and exploitation films of the 1970s and 1980s. "He was very respectful of all the actors in all the movies," Mr Braunstein said. "You couldn't mention a movie that he didn't know everything about."
Sage Stallone also directed the 2006 short Vic, which screened at the Palm Springs Film Festival.
Mr Braunstein said the actor was planning to marry for the first time, and had frequent requests to work on films. "He was a full-of-life film-maker with his whole future ahead of him. He was just very enthusiastic and positive." Speaking about the death, he said: "I think it was probably some sort of accident."
Mr Braunstein said Sage Stallone greatly admired his father but was working hard to make his own name in the film industry. "He was very proud of his father and proud to be his father's son," he said.