A new ITV documentary, West and Hindley: The Untold Story, is set to delve into the little known affair between murderers Rose West and Myra Hindley, with Sir Trevor McDonald presenting.
The two women are both infamous for being the worst female serial killers this country has seen.
Moors murderer Hindley killed five children in cold the 1960s alongside her lover Ian Brady, meanwhile West was found guilty of 10 equally horrific murders alongside her husband, Fred West - and one of the victims was even her own daughter.
But what people don't know is the story of what happened after they ended up in jail, as the only two women to be given whole life sentences behind bars, meaning they'll never be released.
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On conviction West, 41, was sent to the H 'Hell Wing' in HMP Durham, which is where 52-year-old Hindley also resided, alongside many of Britain's most serious female prisoners, including IRA terrorists, sex offenders, and arsonists.
There, the women formed a tight bond, having both committed similar crimes, and their close friendship even developed into an affair.
But their relationship cooled off as they battled for the position of jail royalty, and they went from confidantes to rivals.
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Featuring exclusive interviews with category A prisoners and previously unseen material the doc will see Sir Trevor shine a fresh light on the pair's unexpected relationship.
It will also look at how the duo behaved individually when they were sent to jail, and prove that they really were evil to the bone.
Trevor learns how Hindley continued to manipulate people from behind bars, much like the children she abducted.
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At one point, she even managed to persuade a nun-turned-prison guard to help her escape from the facility, using her powers of persuasion.
Plus, he hears how West had bouts of anger much like she was known for in the outside world, and still heavily depended on her children from behind bars.
West And Hindley: The Untold Story lands on ITV this autumn
Topics: True Crime, TV News, TV Entertainment