Gary Garland-Houston revealed in new documentary, Whitney, that he and superstar sister, Whitney Houston, were molested as children by Dee Dee Warwick, the sister of Dionne Warwick. Warwick and Cissy Houston were unaware of the accusations until the film was close to wrapping production, with both of them expressing their disbelief in Gary’s claim.

In a new interview with Larry King, Warwick calls the allegation “evil” and “total hogwash.”

“I have tried to refrain from responding to that,” the 77-year-old singer explained. “First of all, it’s totally hogwash. My sister would never, ever have done anything to do any harm to any child, especially within our family. And for those lies to be perpetuated in this so-called documentary film, I think it’s evil.”

“I will never, and I mean this, ever forgive those who perpetuated this insanity,” Dionne added.

Whitney’s longtime assistant, Mary Jones, backed up Gary’s claims, saying the legendary vocalist revealed to her privately that she had been sexually abused by Dee Dee as a child.

Cissy expressed her shock over the claims to PEOPLE two days before the film’s May 16 premiere in Cannes.

“We cannot…overstate the shock and horror we feel and the difficulty we have believing that my niece Dee Dee Warwick (Dionne’s sister) molested two of my three children.”