Speculation that Whitney Houston was bisexual and enjoyed a romantic relationship with her personal assistant and long-time friend Robyn Crawford has been filling gossip columns for years. Now a new documentary has claimed that the late I Will Always Love You hitmaker spiralled out of control after losing the one person that kept her grounded in her bid to appease her family and her religion.

Houston was found dead in her Beverly Hills hotel suite on the eve of the Grammy Awards in February 2012. The official coroner's report ruled that she accidentally drowned in a bathtub because of heart disease and chronic cocaine use.

Co-directed by veteran documentarians Nick Broomfield and Rudi Dolezal, the unauthorised film entitled Whitney: Can I Be Me combines archive material with old and new interviews to tell the story of the rise and tragic fall of the global phenomenon, whose battle with drugs eventually killed her. The narrative is also framed with previously unseen footage from her 1999 world tour, considered by some to be the peak of her career.

Explaining why he took on the project Broomfield – director of Kurt & Courtney, Biggie & Tupac and Heidi Fleiss: Hollywood Madam – told Entertainment Weekly: There's been a lot of stuff done on Whitney, but if you look at them, they're pretty much the same story but I became more obsessed with the fact that she was this incredible crossover artist. Clive Davis' genius was to market her to white teenage girls, and she eventually paved the way for Beyoncé. But that took its toll, and she paid this price for it."

According to People, the documentary delves into the superstar's close friendship with Crawford – which was the target of innuendo-based rumours – suggesting that its collapse was the beginning of Houston's self-destruction. Crawford, who is openly gay, reportedly resigned from Houston's production company in 2000.

"I don't think she was gay, I think she was bisexual," stylist Ellin Lavar said in the movie, according to People.

"Robyn provided a safe place for her... in that Whitney found safety and solace."

"That was the downfall of Whitney. Robyn was the person who was keeping her together."

People reports that in the documentary, her former bodyguard, Kevin Ammons describes the pair as being "like twins". He said: "They were inseparable. They had a bond and Bobby Brown could never remove Robyn. He wanted to be the man in the relationship."

The Hollywood Reporter adds that another person claims she "died of a broken heart."

Houston herself refuted the lesbian rumours in a 1987 interview with TIME magazine, describing Crawford as the "sister I never had." She said at the time: "People see Robyn with me, and they draw their own conclusions. Anyway, whose business is it if you're gay or like dogs? What others do shouldn't matter. Let people talk. It doesn't bother me because I know I'm not gay. I don't care."

Whitney: Can I Be Me debuted at the Tribeca Film Festival ahead of its premiere on Showtime in August 2017.