Graham Boal, for the prosecution, said that Carolyn Taylor, 54, met Gaeton Beisy, 56, while on holiday in Corsica and a month later he moved into her large Surrey home.
She fell instantly in love with him and he scarcely let her out of his sight, he said.
But less than a year later Mrs Taylor's son, Mark, 24, woke at her home in South Holmwood near Dorking to hear his mother screaming. He found her in the hallway, naked and with her face covered in blood.
She had been punched in the face by the Frenchman during a row, the jury was told. As Mr Taylor tried to call a doctor, Mr Beisy appeared with a knife concealed behind his back, Mr Boal said. Mr Taylor tried to get his mother behind him.
'What happened then was dreadfully and fatally simple. Beisy lunged towards her with the knife and pushed it into her,' Mr Boal said.
Mrs Taylor died from a seven- inch stab wound that punctured her lung and went into her heart.
Afterwards, Mr Beisy allegedly told Mr Taylor: 'I have killed your mother - your mother has been sleeping around.'
He then tried to stab Mr Taylor, the court was told.
Mr Beisy denies murdering Mrs Taylor on 15 July last year and attempting to murder her son.
After the killing, Mr Beisy disappeared with a bottle of whisky and one of port. He was later found unconscious in a field with the knife beside him.
Later, in police custody, he tried to commit suicide by cutting his arms with glass from his spectacles. 'Knowing what he had done, he attempted to take his own life,' Mr Boal said.
He said that Mrs Taylor's husband died from cancer in 1990. In 1991 she went on holiday to Corsica with her daughter, Samantha.
'There, in what no doubt was a somewhat romantic atmosphere, she met the defendant, who was making a living flying a two-seater plane from the beach. . .'
Mr Taylor told the court his mother and Mr Beisy seemed very happy together. Mr Beisy did jobs round the house and most of the cooking, and Mr Taylor said he thought he 'loved her very dearly'.
'He was very considerate to her. But he was very possessive with her. If she was in the company of another man, he did not like it.'
Mr Taylor denied that he was responsible for punching and knifing his mother.
Rosina Hare QC, for the defence, put to him that he and his sister were worried 'you were going to lose your home and lose out on any money you were going to inherit'.
He also denied he had gone into the couple's bedroom on the night of the killing and said that his mother was doing a great deal for Mr Beisy and nothing for her children.
The trial continues.