A woman suffocated her two young children and placed their bodies in holdalls in the boot of her car following the breakdown of her relationship with their father, a court has heard.
Fiona Donnison, 45, had moved out of the family home in Heathfield, East Sussex, without telling Paul Donnison six months earlier, jurors at Lewes Crown Court were told.
Opening the trial, prosecutor Christine Laing QC said it was the Crown's case that Donnison killed three-year-old Harry and two-year-old Elise Donnison in order to hurt their father in the most extreme way possible.
Ms Laing said: "This is understandably a complex case particularly in relation to the motive. We say that responsibility lies not as a result of any mental illness but we say as a result of her personality."
She said Donnison, who was not married to the children's father but had changed her name by deed poll, was a narcissist with an overdeveloped sense of self importance and entitlement.
The couple, who had met in 1999 when both were married to other people, had an often strained relationship which was exacerbated by issues concerning her two teenage sons who lived with them and the thousands of pounds worth of debt she was prone to accumulating.
Donnison was also jealous and controlling of her partner, and often exhibited highly manipulative behaviour, the court heard.
Ms Laing told jurors she will claim she lived in fear of Mr Donnison, who she said was prone to losing his temper and often punched walls in frustration.
"Why any of this resulted in the defendant killing the children, she had not said. She claims to have no memory at all of the events that led to the killing of Harry and Elise."
Donnison denies two charges of murder.