Michael Jackson named Diana Ross as a possible guardian of his children because she owed him a "favour".
The late pop star wanted the former Supremes singer to care for his children, should anything happen to his mother Katherine Jackson, because the 65-year-old star needed to repay him for the impact he had on her life.
Michael's long-term friend and journalist John Randy Taraborrelli says the 'Thriller' singer chose his "surrogate mother" Diana to look after his three children - Prince Michael, 12, Paris, 11, and seven-year-old Prince Michael II - because Michael taught Diana what was really important in life when they lived together years ago.
In Taraborrelli's book 'Michael Jackson: The Magic And The Madness' said: "Perhaps Michael - by reminding her with his presence in her home of the important things in life - had inspired her as much as she had inspired him. If so, it is a favour that, 40 years later, his will - naming Diana as the woman he wanted to bring up his children in the event of his mother's death - puts her in a position to repay."
Michael's friendship with the glamorous singer first developed when Michael moved into her Hollywood Hills home as a child, when the Jackson 5 were first discovered.
Taraborrelli explained: "The brothers, newly arrived in Los Angeles, were shuffling from one hotel to another, and it was decided by the record company that Michael needed some stability. They also hoped it would be good for him to be around her."
However, the demands of looking after a child and juggling her growing career took their toll on Diana.
The author explained: "Consumed by the demands of her own career, she probably wasn't prepared for the role of surrogate mother. Still, she gave it everything she had, treated Michael like a son and became attached to him.
"Michael's fascination with Diana - some would later see it as an obsession - would last for many years. She was not only a mother figure when his own was thousands of miles away, she was an accomplished performer whom he studied constantly.
"He told her, 'I want to be just like you, Diana.' She said, 'You just be yourself.' "
However, Katherine - who Michael has given 40 per cent of his estate to - was frustrated another woman had taken on her maternal duties.
Taraborrelli explained: "When it was time for Michael to go back to his family, Diana was crestfallen, particularly after Katherine thanked her profusely for what she had done, but then added, pointedly, 'He needs his mother.'
"Diana, whose life had been devoted entirely to her career since she was 15, seemed put out by the reminder that she might no longer be as influential in young Michael's life. She had loved being his 'mother', even for such a short time. She would miss it."