Crane driver Dempsey Nibbs killed his partner of 30 years after he suspected her of having affairs, the court heard.
Judith Nibbs, 60, described as "bubbly and happy", had predicted her own death, telling colleagues, "If I'm not in on Friday, I might be dead", jurors were told.
Mr Nibbs, 69, of the Charles Estate in Hoxton, denies murder.
The court heard that Mr Nibbs carried out the act because he thought his partner was a "snake", and said he had killed her while "defending himself".
Crispin Aylett QC, prosecuting, said the couple's relationship had soured in the spring of 2014 as Mr Nibbs suspected his partner of infidelity.
Ms Nibbs had confided in her sister and a colleague at Meals on Wheels that her partner had threatened to kill her and grabbed her by the throat.
During a row on 7 April, she had taunted Mr Nibbs with details of her infidelities, saying: "I have had sex eight times."
On the night of 10 April, Mr Nibbs attacked her in their Hoxton flat and knocked her out, Mr Aylett said.
"Having attacked his wife, the defendant then took up a kitchen knife and cut off her head," he said.
The court heard how Mr Nibbs disposed of remains down the lavatory, before writing a suicide note to his son and ringing police to tell them they would find "a couple of dead bodies" at his home.
The trial heard that Mr Nibbs shown no signs of mental illness in the wake of the killing.
Ms Nibbs's former workmates described her as a happy, joyful, bubbly and open-minded woman.
The trial continues.
A jealous man beheaded the mother of his two children in an act of "pure hatred", the Old Bailey heard.