The singer - who married the late 'Thriller' hitmaker in 1994, before splitting in 1996 - believes she may have been able to help Michael and regrets she never made a phone call to him in his time of need.
When asked by Oprah Winfrey on her TV talk show if she could have saved him, Lisa Marie replied: "I know it's naive to think that I could have but I wanted to. Had I made a call, had I stopped being so shut off from him, had I just said 'How are you?' I really regret that I didn't."
However, despite her guilt, she thinks his death was inevitable, saying: "I think that was a train heading in a certain direction that no one could have stopped. I've had to really get my head around that in order to stop the pain."
She also revealed how Michael wouldn't let anybody get close enough to help him and pushed everyone away.
She said: "If he didn't want you around, if you were going to make him confront something he didn't want to confront, he could make you go away - including his own family."
Michael died of acute Propofol intoxication at his home in Los Angeles on June 25 last year.