'American Idol' Contestant Doug Kiker Cause of Death Released

"American Idol" alum Doug Kiker -- who was known by the moniker "The Singing Garbage Man" -- died from an opioid overdose, TMZ has learned.

According to the City and County of Denver Medical Examiner's report obtained by TMZ, Doug died from the combined toxic effects of fentanyl, methadone, and amphetamines, with recent cocaine use -- and his death has been ruled an accident.

Kiker died last month, as confirmed to TMZ by his brother William and mother Joyce -- with his ex-fiancée, Valerie Cook, telling us she hates that her kids lost their father.

As TMZ reported in March ... law enforcement sources told us a pedestrian in Denver noticed Kiker on the street and was concerned about his appearance, thinking he might have been experiencing a drug overdose, and called 911. Paramedics responded and rushed Kiker to a hospital, where he died five days later.

Doug’s death was so sudden and shocking that his sister, Angela Evans, launched a GoFundMe, saying the family needed help covering memorial costs.

Kiker famously brought Katy Perry to tears with his rendition of Rascal Flatts’ “Bless the Broken Road” during Season 18 of American Idol, earning him a spot in the Hollywood round.

He was cut in the next round after performing Marvin Gaye's "Ain't No Mountain High Enough."

He was 32.