The 23-year-old model and actor died on July 4.
Daniel Mickelson's cause of death has been determined. The actor and model died of an overdose on July 4, at the age of 23.
The L.A. County Medical Examiner confirmed to ET that Mickelson due to fentanyl and cocaine toxicity. The manner of death has been ruled an accident.
Mickelson's death was first revealed by his sister, model Meredith Mickelson, who shared the heartbreaking news on Instagram on July 5.
"My heart is shattered & to write this feels so wrong and I don’t even know what to say. Yesterday i lost my brother, best friend & the other half of my heart. There wasn’t a person i loved more on this earth," the model wrote next to a photo of her and Daniel as children.
"There's no words that can do him justice that I could write. To know him was to love him," she continued. "He was the happiest brightest smiley most sunshine human to exist and I’m so happy God chose me to be his sister for his whole amazing life."
Daniel appeared in the 2019 film The Killer Clown Meets the Candy Man as well as the series Mani. He was also the founder of clothing brand Kids Back Home.
Mickelson's death is the latest in a string of high-profile accidental drug overdoses in which fentanyl has played a role. It was determined that Michael K. Williams' death earlier this month was a result of ingesting fentanyl-laced heroin and cocaine. Fentanyl also played a factor in the deaths of Prince, Michael Jackson and Tom Petty, among several others.