Bobby Brown to Open up About Daughter Bobbi Kristina's Death in '20/20' Interview

Two months ago, Nick Gordon sat down with Dr. Phil to talk about Bobbi Kristina Brown's death. Now, Brown's father Bobby is stepping forward to tell his side of the story, and things are getting complicated.

In a special 20/20 interview airing tomorrow, Bobby sits down with ABC's Robin Roberts to talk about the death of his daughter, as well Gordon's alleged relation to it. Bobbi Kristina died on July 26, 2015, from lobar pneumonia and lack of oxygen resulting in brain damage after she was found unconscious in a bathtub. She was in a coma for six months before her death.

"It's not a mystery to me," Bobby told Roberts of his daughter's passing in a preview to the episode. "The same thing that happened to my daughter is what happened to Whitney. ... There’s only one person that was around both occasions, only one person who says they were there to protect them ... and he didn’t." No criminal charges have been filed against Gordon at this time.

"The last thing I told her, I just said, 'Let go.' I said, 'It's OK, you can go with your mom. Daddy’ll be all right. I love you. You can rest now,'" Bobby said of his daughter. "Hardest thing I had to do in my life was tell my daughter to let go. ... I don't wish that on my worst enemy or any enemy. That is the worst pain in the world."

Bobby's new book, Every Little Step, comes out on Monday, June 13. Watch the preview to his 20/20 episode, airing tomorrow, here.