Joan Rivers' cause of death is no longer unknown.

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According to the former Fashion Police star's autopsy results, Rivers experienced a "therapeutic complication" and suffered brain damage due to a lack of oxygen, which resulted in her September 4 death, Us Weekly reported Thursday.

Rivers, who had starred in Joan & Melissa: Joan Knows Best?, went into cardiac arrest on August 28 during a routine medical procedure at Yorkville Endoscopy outpatient clinic in New York City to check out her voice's raspy sound and reflux.

"[Office of the Chief Medical Examiner] has completed its investigation. The cause of Ms. Rivers' death is anoxic encephalopathy due to hypoxic arrest during laryngoscopy and upper gastrointestinal endoscopy with propofol sedation for evaluation of voice changes and gastroesophageal reflux disease," OCME representative Julie Bolcer said in a statement obtained by Us.

"The manner of death is therapeutic complication. The classification of a death as a therapeutic complication means that the death resulted from a predictable complication of medical therapy."

The Celebrity Apprentice's second-season winner died at the age of 81 at Mount Sinai Hospital about one week after she underwent her minor throat procedure because her daughter Melissa Rivers had reportedly taken her off life support.