John Egerton called the ambulance and police after discovering his mother Kathleen Egerton, 39, a former local councillor, in Morecambe, Lancashire, had been shot in the head with a self-loading pistol belonging to her husband Philip, 47, said police.
Mr Egerton, who also had a gunshot wound to the head, was taken to hospital in Lancaster but died shortly afterwards.
Police said they were not seeking anyone in connection with the tragedy.
John Egerton was said to be severely shocked and was being cared for by relatives and social workers today.
Lancashire police said the weapon found in the house was registered in Mr Egerton's name. A former chiropodist, Mr Egerton was a member of a local gun club and was licensed to use the small handgun with which he and his wife were shot.
Three other licensed weapons, all kept secure in accordance with gun rules, were found in the house.
Detective Inspector Neil Smith said: "There is some evidence the couple seemed to be having some matrimonial difficulties. But we may never know how this happened."
He said police were not looking for anyone and were working on the theory that Mr Egerton shot his wife before turning the gun on himself.
Mr Smith said that John, the couple's only son, was with a 13-year-old friend in a room at the front of the house when they heard two shots at around 5.30pm and called the emergency services.
John was staying with relatives yesterday and was said to be seriously traumatised. The two boys are to receive counselling over their ordeal. Detectives have still to interview them over what happened.
Mr Smith said he was not aware of any other person being involved in the couple's problems. "They seem to have been general domestic difficulties," he added.
Mr Egerton had given up his chiropody business to take a job at the nearby Heysham nuclear power station, but had taken redundancy and used some of the money to buy sheltered accommodation which he rented out.
His wife had a share in a residential home in the area and recently went into partnership to open a new nightclub, The Galleon, in the resort.
Mrs Egerton was a member of the Morecambe Independent Group on Lancaster City Council until the last elections when she did not stand, apparently over a policy difference.
The shootings shocked the community of Bare in Morecambe, where the couple were well-known as friendly and pleasant.
A man living opposite said: "It is unbelievable it could happen. She was a very bubbly, outgoing personality but her husband was the opposite and was very quiet."Reuse content