Bobby Brown Says He & Whitney Houston Let Bobbi Kristina Down

It's been a little less than a year since Bobbi Kristina Brown passed away. In the intervening months, her official cause of death was revealed to have been water immersion and mixed drugs. But her father, Bobby Brown, has another angle on what really happened to his daughter. "It's not a mystery to me," he said in an interview with ABC's Robin Roberts, set to air on 20/20 Tuesday night, as People reports. "The same thing that happened to my daughter is what happened to Whitney." Indeed, Houston's official COD was drowning due to atherosclerotic heart disease and cocaine use. But Brown also says that both he and his ex-wife contributed to their daughter's demise by failing her as parents. "We could have been better," he admitted. "We should have been better." That said, while Brown does accept some responsibility in his daughter's untimely death, he still believes that her boyfriend, Nick Gordon, is mostly to blame. "He knows what happened," Brown said of Gordon. "I don't know what happened that night. But he does." For his part, Gordon denies any wrongdoing, and went on record with the Daily Mail earlier this year about what happened the day that Bobbi Kristina was found in the bathtub. He has not been charged with any crime in relation to her death. Gordon does, however, accept a certain level of responsibility for being unable to save the then 21-year-old. "I did not protect her the way that I was supposed to," he said in late April of this year, "Even if it was from herself." Bobbi Kristina Brown passed away on July 26, 2015, at home under hospice care. "I just said, 'Let go,'" Brown remembers telling his daughter. "I said, 'It’s okay, you can go with your mom, daddy’ll be all right. I love you. You can rest now.' "Hardest thing I had to do in my life was tell my daughter to let go," he went on. "I don’t wish that on my worst enemy or any enemy. That is the worst pain in the world."