Whitney, filmmaker Kevin Macdonald's new authorized documentary about legendary singer Whitney Houston, premiered at the Cannes Film Festival on Wednesday (May 16), and although the film won't be in theaters until July 6, some of its revelations are coming to light now. Sadly, the most serious is an allegation of childhood sexual abuse: According to Houston's half-brother Gary, who spoke to Macdonald for the film, both he and Houston were molested as children by Dee Dee Warwick, a niece of Houston's mother Cissy Houston and the sister of singer Dionne Warwick. Whitney Houston's former assistant, Mary Jones, said Houston confided in her about a childhood experience of sexual abuse by a woman, saying she never told her mother about what happened. Dee Dee Warwick, herself a soul singer who backed up Aretha Franklin, died in 2008 at age 63. Houston died in 2012 at age 48. Cissy Houston and Dionne Warwick have been informed about what's in the new documentary, but haven't yet watched it in full, Macdonald told Vanity Fair. Macdonald felt compelled to work on the film, he said, after watching hours of unreleased Houston footage that caused him to wonder if the singer harbored a painful secret that might help explain her struggles with addiction and troubled final years. At first, he thought it might be her own sexuality: Macdonald says he's seen documentation proving Houston had a short (albeit long-rumored) romantic relationship with her close friend Robyn Crawford. "The real story, as I dug deeper, had to do with her family, and to do with race, I suppose, and her childhood," he said, and the new documentary touches on multiple aspects of Houston's upbringing and sometimes strained family relationships. Read Vanity Fair's full interview with Kevin Macdonald about the making of Whitney here.