Jack Osbourne got emotional revealing how he learned his father Ozzy Osbourne had suddenly passed.

He opened up about the heartbreaking moment in a YouTube video posted on his channel Wednesday ... revealing a person who had worked for his family for 30 years came knocking on the door of his Los Angeles home at 3:45 in the morning to tell him the sad news. Gallery Launch Gallery Getty

Jack -- visibly holding back tears -- said he immediately felt "sad and frustrated and angry" over Ozzy's passing, but felt comforted knowing his father was no longer suffering.

The Black Sabbath legend died of a heart attack on July 22 ... he also suffered from coronary artery disease and Parkinson’s disease. Play video content

Jack said his father "was having a rough go" before he died

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