"American Idol" alum and Grammy-winning singer Mandisa died earlier this year -- and now, we know how ... as we've obtained her autopsy report.

TMZ obtained a copy of the document which lists Mandisa's official cause of death as "complications of class III obesity," with the medical examiner noting she weighed 488 pounds at the time of her death.

Per the report, the singer's friends found her in a state of decomposition in her residence on April 18. Emergency medical services arrived at the scene, where she was pronounced dead.

Despite her state of decomposition, the autopsy was able to be thoroughly conducted ... which showed no signs of trauma to her neck. A toxicology report also found nothing abnormal ... resulting in the manner of death being ruled as natural.

As we reported ... Mandisa was found dead in her home in Nashville this past April. Mandisa's passing at 47 sent shockwaves through her fans and loved ones ... and her father told us she had no known health issues prior to her sudden passing.

Though, as detailed in the new report, her past medical records indicated a history of ulcerative colitis, sleeve gastrectomy and obesity.

She had previously opened up about her mental health struggles, telling ABC News in 2017 she'd contemplated suicide before. Her mental health struggles did not play a factor in her death, however.

Mandisa rose to fame in season 5 of 'Idol' in 2006, finishing in 9th place. She was hugely successful in the faith-based music community ... winning the Best Contemporary Christian Grammy for her 2014 single, "Overcomer."

She was 47.