"An actress named Holly Brooke, who has been described in most books about Mickey as a showgirl who had been his girlfriend in 1951,” Castro said in an interview about writing the book. “However, no biographer had been able to interview her or even locate her. I think most of us had assumed she was dead. Holly’s nephew, though, said not only was she still alive and well but that she was also willing to talk to me.
“That began a series of almost daily visits and conversations that proved to be incredible. She convinced me with her stories and some strong documentation that her love affair with Mickey lasted beyond his marriage in 1951 and carried on well into the 1960s.”
Holly had lived with Mantle much of his rookie year, even when he was sent down to the minors to play in Kansas City, which had a Yankees’ minor league team at that time. She was also the reason Mickey asked to have his uniform number changed from 6 to 7 when he returned to the majors, a number that was her date of birth."