One of the many photographs Frank Cascio took of Michael Jackson.

When Frank Cascio was 13-years-old, he left home to go on tour with Michael Jackson. He eventually became Jackson’s business adviser and learned that behind the scenes, the King of Pop wasn’t always in control.

Cascio sat down with ABCNews.com to talk about the star’s financial troubles, the real reason he married Debbie Rowe, and the one song that never failed to make Jackson transform:

He also shared a special message for Jackson’s fans and revealed why he wrote his new book, ”My Friend Michael,” on sale now:

Click here for the first installment of ABCNews.com’s interview with Cascio, where he talks about the pranks he and Jackson used to play.  

WATCH: “20/20's” interview with Frank Cascio.