Madonna thought Michael Jackson was "too shy".
The 'Revolver' singer spent weeks working with the 'King of Pop' several years ago, but never recorded a duet with him because Michael was scared of Madonna's "provocative" music.
The 51-year-old star recalled: "We spent a chunk of time together, and became friends, but it never happened. I wrote a bunch of words and presented them to him, and he didn't want to go there.
"He didn't want to be provocative. And I said, 'Well, why come to me?' I mean, that's like asking Quentin Tarantino to not put any violence in his films. I felt like he was too inhibited, too shy."
Madonna paid tribute to Michael - who died in June of acute propofol intoxication - in an emotional speech at the MTV Video Music Awards earlier this month.
Even though she used the occasion to "say goodbye" to her old friend, the star admits she can't stop thinking about Michael, and the torment he faced at the hands of the media.
She told Britain's Times newspaper: "When I heard he had died, the first thing that came into my head was the word 'abandoned'. I feel like we all abandoned him and put him in a box and labelled him as a strange person.
"And it used to pain me to see people go write such horrible things about him, accuse him of being a child molester, and all these things that nobody had any proof of because I've had plenty of things I've been accused of.
"When I adopted David, I was accused of kidnapping him, for God's sakes; and it's very hurtful, and people love to jump on bandwagons. The lynch-mob mentality is pretty scary."