Bobby Brown to discuss Bobbi Kristina and his new book on "20/20" with Robin Roberts

Bobby Brown will discuss the untimely death of his daughter, Bobbi Kristina Brown, and his upcoming book in an interview with Robin Roberts on "20/20."

“We should have been better,” Brown tells Roberts in the interview airing at 10 p.m. Tuesday. “We could have been better.”

PAST COVERAGE: Bobbi Kristina's body was scarred and missing teeth, autopsy showed

Bobby Brown discusses his daughter Bobbi Kristina's death and his new memoir "Every Little Step" with Robin Roberts. Photo ABC/ Rick Rowell

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"The hardest thing I've ever had to do in my life was to tell my daughter to let go," he said.

In this preview Brown, still grief stricken, notes that his daughter and his ex-wife died in tragically similar ways.

"There's only one person who was around both occasions," Brown said.

"Nick Gordon is who you're referring to," Roberts responded, noting the wrongful death lawsuit filed by Bobbi Kristina's estate. Gordon's legal team has blasted the lawsuit as slanderous and meritless.

The lawsuit  alleges financial impropriety and severe physical harm .

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

In March, Gordon's legal team issued a statement saying her death was “was an accident… or even a suicide, but not a murder,” and sought an end to the specter of possible legal or criminal proceedings involving him.

The lawsuit was filed when Bobbi Kristina was still alive and amended after her death. Gordon’s legal team responded seeking a dismissal on numerous grounds – namely that the suit against him lists damning allegations but no police reports, affidavits or other backing evidence.

No charges have been filed against anyone in connection to Bobbi Kristina's death.

Here's the "20/20" preview:

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