06/06/2016 AT 11:10 AM EDT  "We could have been better. We should have been better," Bobby Brown said in a candid interview with ABC News'  , set to air on  at age 22 after being found unresponsive in her bathtub in January 2015. The Fulton County Medical Examiner found she died from a  . A toxicology report found marijuana, alcohol, "a cocaine-related substance," sedatives, anti-anxiety medications and morphine in her system when she was found.  "It's not a mystery to me. The same thing that happened to my daughter is what happened to Whitney," Brown told Roberts.  Despite accepting some blame for himself, added that only one person was around both Houston and Bobbi Kristina near the time of their deaths:  Gordon, 26, was Bobbi Kristina's boyfriend who lived with her at the time she was found unresponsive. He has denied all wrongdoing and has not been charged by authorities in connection with Bobbi Kristina's death.  "He knows what happened," Brown says. "I don't know what happened that night. But he does."  Houston took Gordon in when he was just 12 years old and going through a difficult time. Though Houston never officially adopted him, Gordon was  in Houston's house and was good friends with Bobbi Kristina before they started dating after Houston's death.  "Regardless of what everybody thinks, I made Krissy and Whitney's last few years on earth as happy as they would be," he  in an April episode of  . "I gave them somebody to trust to, to talk to, to be there, someone genuine."  Following Gordon's appearance on the talk show, Brown  his daughter's conservator as a plaintiff in the  The renewed motion states that "the defendant ignores this Court's mandates but freely discusses his role in the incident which led to the horrific injuries to Decedent Bobbi Kristina Brown on public television" and "fully and freely discusses the version of the facts and circumstances which gave rise to this litigation."  Gordon's lawyer has filed motions denying any involvement in Bobbi Kristina's death.  "The last thing I told her, I just said, 'Let go.' I said, 'Itâs OK, you can go with your mom, daddyâll be all right. I love you. You can rest now,'" Brown said. "Hardest thing I had to do in my life was tell my daughter to let goâ¦. I donât wish that on my worst enemy or any enemy. That is the worst pain in the world."  interview will air at 10 p.m. on Tuesday, June 7, on ABC.
Bobby Brown says Nick Gordon was the only one around both his daughter and his ex-wife around their deaths