A man cut off his wife's head with a kitchen knife before he smashed it into pieces and flushed it down the toilet "out of pure hatred", a court has heard.
Dempsey Nibbs, 69, had claimed he decapitated the mother of his two children, Judith Nibbs, 60, because he thought she was a "snake".
But his murder trial heard there was "no evidence" the crane driver was mentally ill following the gruesome killing at the couple's home in Hoxton, east London, in April 2014.
Outlining the case at the Old Bailey, Prosecutor Crispin Aylett, QC told the jury to "brace" themselves.
He said the couple's relationship had run into problems in the spring of 2014 after Nibbs suspected his wife of having affairs.
The victim, who had three children from a previous marriage, had told her sister and a colleague at Meals on Wheels that the accused had threatened to kill her and grabbed her by the throat.
It was during a row on 7 April, that Ms Nibbs admitted seeing other men.
The following day, she told colleagues she feared being killed, saying as she left work: "If I'm not in Friday, I might be dead."
On the night of Thursday, 10 April, Nibbs attacked her in their Hoxton flat and knocked her out, the court heard.
Mr Aylett said: "What might otherwise have been family tragedy now becomes terrible. You will, I am afraid, have to brace yourselves.
"Having attacked his wife, the defendant then took up a kitchen knife and cut off her head.
"Nor does the horror end there: having decapitated his wife, the defendant began to break her head into pieces with a mallet and a metal bar.
"He then flushed the pieces down the lavatory."
The prosecutor added: "Quite why the defendant decapitated Judith and then disposed of her head is not entirely clear but it may well be that he did it out of pure hatred at the sight of his wife's face."
After the killing, Nibbs wrote a suicide note to his son and called police to say they would find "a couple of dead bodies" at his home.
When an officer arrived he saw the headless body through the letter box and kicked the door in.
He found Nibbs in the bathroom with a shotgun in one hand and a kitchen knife in the other which he used to stab himself.
Nibbs was taken to hospital with stab wounds to the neck and stomach.
The defendant, who was also diagnosed with prostate cancer in 2012, was not well enough to be interviewed by police for a year.
Mr Aylett told jurors the defendant admitted killing his partner but claimed he had been "defending himself".
The victim, who took Nibbs' name despite never being formally married, was described by workmates a happy, joyful, bubbly and open-minded woman.
Nibbs, of the Charles Estate, in Hoxton, denies murder and obstructing the coroner from holding an inquest in the violent death of Judith Nibbs by disposing of her decapitated head.