Who is Karrine Stephens referring to as "Papa" in her book ?

Answer 1

If she had gave up the guy's identity, do you think people would still be referring to him only as "Papa"? No, they would call him by his real name.

It wasn't Bobby Brown. Because she named him in her book. Plus, she said she would never give up "Papa's" identity.

Here's a snippet of one of her interviews:

KW: Why were you so very tight-lipped about the nature of your relationships with all the celebrities you knew the first time we spoke?
KS: Well, that wasn’t the appropriate time. We were talking about "A Man Apart". Everything has its own time and space. And there are some people that I mention in Confessions, and some that I still didn’t.
KW: Yeah, like in the book, you hid the identity of a very famous lover of yours you called Papa. Care to share his name now?
KS: I’m still not going to tell you.
KW: Why not, when you’ve confessed to sleeping with so many others?
KS: At this point it’s inappropriate, because of a promise I made to him that he would remain anonymous.
KW: How about a hint?
KS: What I will say for my readers is that Confessions has a really big clue about who he is.

Answer 2

Bobby Brown.