A young mother has become the first British woman to be convicted of allowing her child to be murdered by a violent partner.
Rebecca Lewis, 21, regularly watched her boyfriend beat her 13-month-old son.
On one occasion she allowed him to pick little Aaron up by his ears and throw him across the room.
Andrew Lloyd, 23, once hit the boy so hard that he left him looking 'like the Elephant Man'.
The toddler eventually died from severe brain damage.
Yesterday, in emotionally charged scenes, Lewis was told that she would be jailed for failing to protect and care for Aaron.
There were cheers from the court's public gallery when a jury convicted her of familial homicide - or causing or allowing the death of a child.
The new offence came into force last year as a way of punishing people for not actively stopping a murder from being committed.
Her boyfriend has already admitted killing the little boy.
Swansea Crown Court heard that Lloyd had caused a 'constellation of some 50 injuries' to Aaron's body, which caused extensive bruising and serious brain injury.
It was said that although Lewis was largely absent when the violence was inflicted, her silence allowed it to continue.
Prosecutor Paul Lewis QC - who is no relation to Miss Lewis - said: "Andrew Lloyd systematically and violently assaulted a defenceless child and ultimately killed it.
"Aaron's mother, Rebecca Lewis, should have protected and cared for her son, but she allowed Lloyd's ill-treatment of Aaron to continue until, eventually, her inaction cost him his life."
The court heard that the series of attacks left Aaron looking like 'the Elephant Man', according to a neighbour of the couple.
Lloyd would swear at the boy, threaten to kill him, blow smoke into his face and once promised 'to smash your little head in'.
Giving evidence, Lewis admitted she had seen her boyfriend pick up Aaron by the ears and threw him on the settee at their home.
She added that Lloyd would flick the baby's ears and feet, causing him to scream in pain, and had seen him swing the child around violently by the ankles.
She told the jury that despite realising Lloyd was mistreating Aaron, she still left her boyfriend to look after him in the weeks before his death.
The mother said her son would have bruises on his face when she returned to her home in Swansea, and that Aaron would 'shiver in fright' at the sight of her boyfriend.
But she insisted that she did not believe Lloyd would kill her son, saying: "I did not think that he would seriously harm Aaron, just harm him a bit."
Lewis said she feared she would be harmed or killed if she reported her violent boyfriend's behaviour.
The distressing case is one of just a handful of prosecutions carried out since the offence of familial homicide was introduced.
It was designed to close a legal loophole that allows a couple jointly accused of murdering a child to escape justice by remaining silent or blaming each other.
Earlier this year, an asylum seeker from Zimbabwe became the first person to be convicted of the offence.
Sandra Mujuru, 21, escaped jail after she left her young daughter Ayesha in the care of her boyfriend Jerry Stephens, who went on to kill her.
Yesterday a spokesman for South Wales Police said of Lewis's case: "We are pleased to see justice being served and those responsible for depriving Aaron of the chance of living a happy and meaningful life will now face the consequences of their evil doings.
"This has been an extremely emotional case for everyone as no-one could imagine the pain that young Aaron had endured during his short life."
Lewis was remanded in custody and will be sentenced alongside Lloyd on a date to be fixed.