Sylvester Stallone's eldest son Sage died from heart failure, the Los Angeles county coroner's office revealed on Thursday.
Sage Moonblood Stallone (36), who was an actor, producer and director, was found dead at his home in Hollywood on 13 July.
Some bottles of prescription medication were removed from the apartment – sparking speculation that Sage had overdosed – but the coroner revealed that only a "sub-therapeutic" level of a painkiller was found in his body.
The Los Angeles County Coroner's Department has listed Sage's cause of death as Atherosclerotic Coronary Artery Disease – which causes hardening of the arteries – adding that he suffered from no other conditions and describing the death as "natural".
"Toxicology was negative except for a sub-therapeutic level of [painkiller] Hydrocodone," read a short statement from the coroner's office, which indicated that a full report on Sage's death would be published within the next week.
Sylvester (66), was told of his son's death while he was at Comic-Con in San Diego, and at the time said there was "no greater pain" than losing a child, and condemned "speculation and questionable reporting" which suggested that his son – who was actively planning his own wedding in Las Vegas at the time of his death – had committed suicide.
Sage appeared in two films with his father – the 1990 film Rocky V as Rocky Balboa Jr, the son of his father's title character, and in the 1996 movie Daylight.
He is credited with 13 big-screen roles as an actor and served as a producer on three films, including the 2006 short Vic, which he also wrote and directed.