A 23-year-old woman, who was forced to pretend to be disabled from childhood, ordered her mother to be stabbed to death before announcing on Facebook “the b**** is dead.”

Gypsy Rose Blanchard, who had been wheelchair-bound for 10 years, was found guilty, along with her boyfriend, for her role in the murder of her 48-year-old mother Dee Dee Blanchard in June 2015.

However she accepted a 10-year plea deal for second degree murder after Blanchard’s attorney revealed her mother had forced her to pretend to be disabled since childhood.

Rod Blanchard, Blanchard's father and Ms Blanchard's ex-husband, told the New York Post he was in "total shock" when he saw his daughter walk into the courtroom, the first time he realised she was not actually disabled.

Blanchard was forced into a wheelchair and held prisoner for years in the home she shared with her mother in Springfield, Missouri, her attorney told the court at the time.

Her mother had claimed she had been suffering from a host of illnesses, including leukemia as a young child, and later muscular dystrophy.

“I really, genuinely believed that she had some issues,” Mr Blanchard said.

“Dee Dee was really good at convincing me that there was a problem. I never, ever can fathom that she was really in the hospitals, and the doctors wouldn’t have caught on to something at some point over the years.”

The unimaginable story has now become the subject of a new HBO documentary, “Mommy Dead and Dearest.”

The film explores the relationship between mother and daughter and Ms Blanchard’s motivation for making her daughter pretend she was disabled.

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Munchausen by proxy syndrome has been offered as an explanation for Ms Blanchard’s behaviour, a psychological condition in which a person acts as if an individual in their care has a physical or mental illness despite them being in fine health.

However others claim Ms Blanchard imprisoned her daughter in order to collect thousands of dollars in benefits payouts and donations from wellwishers.

The documentary will air on 15 May on HBO.