Klein passed away on Thursday, days after being admitted to a Palm Springs hospital. Law enforcement told TMZ that he was struggling with severe abdominal pains.
Klein, who was suffering from multiple sclerosis, was in a wheelchair when he arrived at the hospital.
Arnold, a famed Beverly Hill dermatologist, is known for prescribing various narcotic drugs to Michael over the years, such as Demerol. After Michael's death in 2009, his reputation was in shambles and he ended up filing for bankruptcy.
Over the years, rumors have swirled that Klein could be the biological father of Michael's son Prince, who recently addressed the rumors on Twitter. When someone said, "everyone knows you are a Rowe-Klein NOT A Jackson!!” Prince responded, "The blood of the covenant is thicker than the water of the womb... I was raised by my dad with my brother and sister."