A 59-year-old woman from Kent killed her husband with an axe after discovering he had fathered a child with her niece, a court has been told.
Wadanahalugeder Chandrasekera, of Port Close, Bearsted, admitted the manslaughter of her husband Sarath, 57, who died from multiple injuries.
Chandrasekera was originally charged with murder but the prosecution accepted her guilty manslaughter plea.
Woolwich Crown Court remanded her in custody until 22 August for sentencing.
The court was told on Thursday that although the couple's marriage appeared to be "as good as over" when Mr Chandrasekera moved into another bedroom in the early 1990s, his wife hoped they would get back together.
But, after he moved out and filed for divorce, she discovered he and her niece were living together and that they had a daughter.
On 22 October last year, Mr Chandrasekera returned to the family home to see his son.
His wife grabbed an axe from the kitchen cupboard and "rained 11 separate, hard blows on him", said Alan Kent, prosecuting.
The court was told doctors agree that at the time of the killing Chandrasekera had an abnormality of mind that impaired her responsibility for her actions.
Chandrasekera, a health visitor, arrived in the UK from Sri Lanka in 1976, a year after her marriage.
On the night of the killing, she told police: "I snapped - I was a crazy woman."
Chandrasekera has been remanded in custody until she is sentenced at the Old Bailey.