Coping with the death of Bobbi Kristina Brown has been an extremely difficult and emotional roller coaster for her father, Bobby Brown.

In a new interview for 20/20 on ABC News, Brown spoke candidly about how he feels that he and Whitney Houston, together, failed their daughter.

“We could have been better,” he told Robin Roberts during the exclusive interview. “We should have been better.”

Bobbi Kristina was found unresponsive in her bathtub in January 2015 and passed away last July at the age of 22. As reported, the medical examiner found the cause of death to be a combination of drowning and drug intoxication. 

"It's not a mystery to me,” Brown continued. “The same thing that happened to my daughter is what happened to Whitney.”

During the interview, Brown also spoke about Bobbi Kristina’s boyfriend, Nick Gordon, who lived with her during the time of the incident. While Gordon has not been charged by authorities in connection with Bobbi Kristina’s death, Brown has plenty of questions for him, some that may never find answers. Brown's suspicions about Gordon's knowledge and possible involvement with his daughter's death has also led him to filing a lawsuit against Gordon.

"He knows what happened," Brown said. "I don't know what happened that night. But he does." 

"The last thing I told her, I just said, 'Let go,’” Brown recalls during the interview. “I said, 'It’s OK, 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.… I don’t wish that on my worst enemy or any enemy. That is the worst pain in the world.”

The interview is scheduled to air tomorrow evening, Tuesday, June 7, at 10 p.m. on ABC.