'The Ring' Star Daveigh Chase's Official Cause of Death Revealed

Daveigh Chase's official cause of death has been revealed ... and the former child star died from AIDS ... TMZ has confirmed.

The L.A. County Medical Examiner says the primary cause of death was acquired immunodeficiency syndrome ... with chronic polysubstance use -- the repeated use of more than one drug over time -- listed as a significant condition. The manner of death was ruled natural. Us Weekly was first to report on the cause of death.

The heartbreaking update comes nearly two weeks after TMZ broke the news that the "Lilo & Stitch" and "The Ring" actress died on June 16 at just 35.

Immunodeficiency syndrome means your body can’t fight infections ... and as we first reported, Daveigh's boyfriend, Roy Hernandez, initially told us she died from complications related to meningitis and sepsis after spending several days in the hospital.

TMZ later revealed her friends had spent years desperately trying to track her down after she disappeared from the spotlight ... even searching Los Angeles' Skid Row after receiving tips she was living there. We also learned she spent her final years living in an RV with Hernandez before she was hospitalized earlier this month.

We also reported her mother, Cathy Chase, said her daughter's addiction to painkillers began after a motorcycle crash around 2016 ... which marked the beginning of a downward spiral.