Boyce died from "sudden unexpected death in epilepsy," the coroner's office determined after additional testing following an autopsy on July 8, according to the report.
"The manner of death was certified as natural,'' the report said.
A family spokesperson released a statement on July 10 saying that Boyce's "tragic passing was due to a seizure as a result of an ongoing medical condition, and that condition was epilepsy." He was found unresponsive at his home in North Hollywood.
Boyce, who was born and raised in Los Angeles, appeared in the 2010 Adam Sandler film "Grown Ups" before going on to star in the Disney Channel's "Jessie" and the three movies in the "Descendants" franchise.
His family has shared its heartbreak while paying tribute to Boyce, with his mother most recently remembering her son as her "compass."
His father, Victor Boyce, called his son's sudden death "a nightmare I can't wake up from" just days afterward, while thanking fans for the love and support they showed his family. Boyce's grandmother, civil rights pioneer Jo Ann Boyce, called him "a shining star" and remembered his "loving nature."
Boyce's younger sister, Maya, 17, wrote about how she lost her best friend.
"Yes, he died. Yes, I’m sad. Cameron was my best friend. He is someone I will always idolize. His smile could light up a room, unlike anyone else’s," she wrote in a note she included in a gallery of candid photographs.
"He was perfect. He always said that if you have a voice, you have the privilege of using that voice for change, and he did not take that idea lightly. He understood his responsibility as someone so many kids would look up to. Cameron always went out of his way to be giving and kind."