Ozzy Osbourne Cause of Death Revealed

Ozzy Osbourne died from a heart attack.

The death certificate is in for the Prince of Darkness and it also says coronary artery disease and Parkinson's were contributing factors ... according to a document obtained by the New York Times.

As we reported ... Ozzy died July 22 and his family said he was with his loved ones, "surrounded by love."

Ozzy's death came only a couple weeks after he took the stage one final time with his band, Black Sabbath. The group's original members got together for a benefit concert at Villa Park in Birmingham, England.

Days before his death, Ozzy was on video sitting down for breakfast with his family ... and he appeared cheerful as he scrolled his iPad at his mansion in Buckinghamshire. His daughter, Kelly Osbourne, playfully commanded him to greet everyone as she recorded.

Ozzy -- dressed in a black tee and headphones -- dutifully responded with an enthusiastic "Good morning!"

The "Crazy Train" hitmaker was diagnosed with Parkinson's disease way back in 2003.