A former Ukip councillor strangled his wife to death after she discovered he was having an affair with their daughter-in-law, a court heard.
Stephen Searle, 64, denies the murder of his 62-year-old wife Anne Searle and is on trial at Ipswich Crown Court.
Ex-Royal Marine Searle says he was acting in self-defence.
Andrew Jackson, prosecuting, said Searle called police on December 30 last year and told the call-handler: "I've just killed my wife."
"Asked by the call handler how he killed her, he said he had suffocated her," Mr Jackson said.
Mrs Searle was found dead at their home in The Brickfields, Stowmarket, Suffolk, minutes after the call made at 10.19pm.
"It's the prosecution case that the killing of his wife was done quite deliberately by him strangling Mrs Searle to death," said Mr Jackson.
"Why did he, as is alleged, murder his wife?
"The prosecution say that this alleged murder had its roots firmly in the discovery by Mrs Searle that the defendant had been having an affair with their daughter-in-law."
He continued: "The discovery of his infidelity with their daughter-in-law had taken place a few months before December 30, and would have put considerable strain on the marriage.
"The prosecution case is that on that Saturday night there had probably been yet another row between the two of them and in anger the defendant strangled his wife to death."
Searle had been married to his wife for 45 years and they had three sons together.
He worked at a bowling alley alongside one of his sons, Gary.
Gary Searle was in a relationship with a woman who worked there, Anastasia Pomiateeva, and they "had children but never married", Mr Jackson said.
Mr Jackson told Monday's hearing that Searle began to pursue his son's partner Ms Pomiateeva and, while he was serving as a Ukip councillor for Suffolk County Council, he invited her to the council building.
"Over coffee there he told Ms Pomiateeva that he hadn't had sex for a long time," said Mr Jackson.
"He asked if she was happy with his son Gary, and if she would like to make him happy."
He said Searle "persisted in his efforts" for weeks and sent Ms Pomiateeva photos of himself bodybuilding.
Mr Jackson said Searle began a sexual relationship with Ms Pomiateeva in April 2017, and this was kept hidden from the rest of the family, but the relationship was discovered in June 2017.
He said that at Christmas last year Mrs Searle, who worked for a sushi producer, wrote on Facebook: "Happy Christmas to you all. Hope you are doing well. Have a good day. I hope I will still be here in 2018. We will see."
Mr Jackson said that Searle trained in unarmed combat with the Royal Marines and knew how to perform a choke hold.
"It's that technique the prosecution say the defendant probably used to kill his wife," he said.
Judge Mr Justice Green told jurors: "He (Searle) says his actions, which led to the death of Anne Searle, were self-defence."
The trial continues.