A first look at the BBC's new documentary, The Case Of Sally Challen, has now been revealed.
The 65-year-old mum-of-two from Surrey was handed a life sentence after she bludgeoned her husband Richard Challen, 61, to death with a hammer in August 2010 following decades of being controlled and humiliated by him.
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But, in a first for the courts, she later had this sentence reduced to four years after a high-profile appeal, in which she cited Richard's "coercive control" as a defence.
And now a brand new teaser clip has dropped before the BBC documentary hits screens on Monday, in which Sally's son David speaks candidly about coming to terms with the fact his mother killed his father, and the realities of his abusive behaviour.
"I had discovered the extent of the abuse after he died," he says in the new clip, filmed four days before his mother's successful appeal.
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"I didn't have the word abuse because I couldn't call it abuse, nor would I acknowledge it as abuse because I didn't know that's what it was.
"But I do know the way he treated her was horrible."
The footage then cuts to David's partner, who offers some further insight into the painful position Sally's son had found himself in - forced to pick between loyalties to his mother and his late father.
"When he first told me, it was genuinely the night I first met him," he recalls. "We were talking and he explained what had happened, and the thing he said was, he'd lost one parent and he didn't want to lose another".
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Sally's murder appeal was successful thanks to the help of lawyer Harriet Wistrich - co-founder of Justice for Women. David supported her the whole way.
Ultimately, Wistrich used numerous witness statements taken from 2010, emails from Richard to Sally, and months of prison visits and video calls with Sally in order to prove her case.
Her defence told how Richard was unfaithful and called Sally 'crazy' when she pulled him up on it, adding that he controlled little things like what colour clothing Sally wore, how much of her salary she was allowed and how often she spoke.
Plus, it wasn't just mental abuse. Sally also alleges Richard anally raped her on more than one occasion, and forced her into sex when she didn't want it.
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When she eventually plucked up the courage to leave him, it was only short lived.
And when they got back together, Richard went as far as to write a list of conditions Sally had to abide by if she wanted to get back together, banning her from smoking and even interrupting him, and threatening to take the majority of their assets away should she ever leave him again.
After a very contentious trial, Sally was released, and her retrial was later cancelled. But the documentary also shows what a tough road it was to get to that point.
Less than 10 per cent of applications for appeal against conviction are successful, and as the court footage showed, proving that coercive control counted as a partial defence was incredibly difficult considering it had never been done before.
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Following her release, Sally has since spoken publicly about the importance of the 'coercive control' defence.
Speaking at a press conference after her release, Sally said: "Many other women who are victims of abuse as I was, are in prison today serving life sentences. They should not be serving sentences for murder but for manslaughter."
The Case Of Sally Challen airs on BBC Two, Monday at 9pm
Topics: True Crime, BBC, TV News, TV Entertainment