Sage Stallone was found unresponsive in his Los Angeles home Friday by an employee and a relative, and police arrived and confirmed Sage Stallone was dead, Assistant Chief Coroner Ed Winter said.
"Sylvester Stallone is devastated and grief-stricken over the sudden loss of his son," publicist Michelle Bega said in a statement. "His compassion and thoughts are with Sage's mother, Sasha."
The cause of death was not clear.
No suicide note was found, Winter said, though prescription bottles were recovered from the home on Mulholland Drive in the Studio City area. Winter could not say what kind of medication bottles or how many, and whether they had a role in the death.
Winter said an autopsy will be performed in the next few days and investigators will look into Stallone's medical history, but a cause of death was likely to take several weeks while toxicology tests are performed.
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 Stallone in the past day, Braunstein said. He said the employee who found the body was a housekeeper.
Sylvester Stallone appeared Thursday at Comic-Con, the San Diego pop culture festival, to promote his upcoming film "Expendables 2" with friend and co-star Arnold Schwarzenegger. It was not clear whether he had remained at the convention or had returned to Los Angeles 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 Stallone had with first wife Sasha Czack.
"Sage was a very talented and wonderful young man, his loss will be felt forever," Bega said.
Sage Stallone made his acting debut in 1990's "Rocky V" and also appeared with his father in 1996's "Daylight."
Also in 1996, Sage Stallone and 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 80s.
"He was very respectful of all the actors in all the movies," 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.
Braunstein said Stallone was planning on getting married for the first time, and had frequent requests to work on films.
"He was a full of life filmmaker with his whole future ahead of him," Braunstein said. "He was just very up and enthusiastic and positive.
"I think it was probably some sort of accident," he said of the death.
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," Braustein said.
Associated Press Writer Andrew Dalton contributed to this report.