Hugo Rutland, 44, was body-boarding with his son Archie, 13, when the youngster got into difficulties off a beach to the north of Cape of St Vincent, Europe's most south-westerly point.
Mr Rutland, a strong swimmer, went to help his son, who had got out of his depth in rough water, but was soon struggling against the waves himself.
Seeing his father in trouble, Archie tried to rescue him by helping to drag him back to the beach and attempting mouth-to-mouth resuscitation.
Mr Rutland's wife, Claire, 43, their daughter, Eliza, 11, and younger son, Henry, nine, were at the other end of the beach, which was in the Algarve resort of Villa Lara, and were unaware that Mr Rutland was fighting for his life. He died in hospital.
At the family's farmhouse in the village of Littlecote in Wiltshire, Mrs Rutland, who had been married for 15 years, said: "His last act was to hold his son in his arms, then, a minute later, it was reversed and Hugo was in Archie's arms and he was trying to bring him back.
"My greatest fear now is that Archie will think it was his fault. It wasn't at all. He desperately tried to save his dad."
Mrs Rutland explained that her knowledge of the events which led up to her husband's death last Saturday came second-hand from others on the beach and afterwards from Archie.
She said: "Hugo and Archie started off swimming in the centre of the beach but there were some very strong currents. They were together taking the waves, when one of the mothers realised the sea was getting a bit strong and that Archie had got a bit out of his depth and she shouted for everyone to get out of the water.
"My husband grabbed hold of Archie and tried to bring him in and nobody is very clear about what happened after that. We think he must have got cramp. The next thing that happened, he was just floating in the water."
Recalling the events of last Saturday, Mrs Rutland said that she saw a crowd gathering from where she was at the other end of the beach, but that she didn't think it had anything to do with her.
She said: "That's the way it is, though - you never think it's going to be you."
She found out her husband was involved when a friend rushed up to tell her.
She said: "I was just screaming my head off - why didn't they get him off the beach, where was the ambulance, why can nobody take him to a hospital?"
Mrs Rutland added: "Hugo loved life and he loved his family. He always put us first. He had friends everywhere and in every area. He had a magic gift of being able to befriend anybody and everybody. He was my rock and my best friend."
Mr Rutland will be buried near his home next Thursday.Reuse content