The 'No More Drama' hitmaker has confessed she felt drawn to the singer's life and music despite never meeting the late star before she passed away from alcohol poisoning in July 2011.
Mary, 43, hailed Amy a ''rare'' talent and admitted she had developed a deep respect for the singer before she died aged just 27.
In an interview with Stylist magazine, she said: ''I never met Amy so I never got the chance to tell her how much I loved and respected her. I was really rooting for her and wished her well: I was a huge fan.
''I felt a connection to her lyrics and to her life. She spoke the truth from a place of, 'I need help but I'm also trying to enjoy my life.'
''She was just an amazing person and so honest lyrically. Those types of artists are rare. To come along and say something like, 'You tried to make me go to rehab' was unlike anything anyone else had sung about and that was real. I respected that.''
The Grammy Award-winner - who has shared her own struggle with drink, drugs and depression in the past - also opened up about the moment she decided to turn her life around and beat her depression.
She explained: ''I had to make a choice when things got bad. I suffered from depression. I didn't want to die, but I didn't want to live. I knew that if I hurt myself or killed myself, my mom and my family would suffer and I didn't want to leave. I have a conscience and I had to make a choice - and I chose life.''
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