Whitney Houston was allegedly sexually abused by her cousin as a child, a new documentary has claimed.

The 'I Will Always Love You' hitmaker - who was found to have cocaine, marijuana and prescription medication in her system when she accidentally drowned in the bath in February 2012 and died at the age of 48 - is the subject of a new film about her life called 'Whitney'.

The R&B star's assistant Mary Jones - who was the person who discovered her lifeless body - and her half-brother Gary Garland-Houston make the disturbing claims in interviews for the film, with Mary stating Whitney told her that the late Dee-Dee Warwick, the sister of Dionne Warwick, allegedly abused her between the age of eight and nine.

According to Mary, Whitney said: ''Mary, I was [abused] too. It was a woman.''

And when asked who it was, she is claimed to have said: ''It was Dee-Dee Warwick.''

Gary also claims to have been abused by a ''female relative''.

According to The Times newspaper, Whitney's mother Cissy was never told about the alleged abuse, with her aunt claiming she ''was ashamed''.

Mary - who Whitney referred to as 'Aunty Mary' - also claims that the alleged abuse made the singer ''question her sexual preference'', and led to her getting married to Bobby Brown - whom she divorced in 2007 after 10 years of marriage - to show the world she was heterosexual.

A source close to the Warwick family played down the abuse claims stating that Dee-Dee was openly a lesbian in her life.

The family insider said: ''Dee-Dee was openly lesbian in the music industry. Not necessarily in the public, but I don't think that was a secret within the music industry.

''Whitney felt closer to Dee-Dee by virtue of them sharing similar orientation. It is interesting that there is that connection.''

The director of the movie, Kevin Macdonald, revealed that it was only towards the end of shooting that he was made aware of the claims by Mary and Gary.

He told Deadline: ''He told me that he was abused by a woman in the family, and Pat Houston told me that, yes, Whitney had said to her, 'This is what happened.'

''So at that stage, I'd had the confirmation that something had happened, but I didn't know who it was. And then, on the next interview, Gary did tell me who it was. This was at the very end of filming, two weeks before we locked the cut. Then I [interviewed] Mary Jones, who was Whitney's longtime assistant [throughout] the last 10 years of her life, and who knew her better probably better in that period than anybody else. And she told me Whitney's point of view on this, and what Whitney had told her in detail, and how important she felt it was for understanding Whitney, but how scared everyone was to talk about it. So, yeah, the film changed radically in the last weeks of editing it, which I guess, as a detective, is the result you want.''