The late actor reportedly relapsed midway through the production of Season 2 of the hit HBO show.
The coroner's office said the 25-year-old actor died of acute intoxication after an accidental drug overdose.
The 25-year-old actor was found dead at his family’s home in late July.
The Emmy winner had previously honored her late "Euphoria" co-star on Instagram, referring to him as her "brother."
The actor, who played Fez on the hit show, died on July 31 at his family's home in Oakland, California.
The mother of the late "Euphoria" actor broke down his last day and described it as "a joyful one" in a Facebook post on Friday.
Eilish performed a song featured in the hit HBO series during her headlining set at the music festival Thursday.
"I’m so grateful I got the chance to know him in this life," Zendaya wrote of Cloud, who died Monday at age 25.
Cloud is known for his role as Fez on the HBO series "Euphoria."