The death of a five-year-old boy who drowned in a swimming pool while on holiday in the Algarve was an accident, a coroner has ruled.

Rupert Marshall was found face down in the shallow end of the pool while on a break with his two older sisters, their father and his partner.

Despite efforts to revive Rupert by the emergency services and his father's partner, Joanna Gardner, the youngster died on August 21, 2013.

The holiday at Ms Gardner's mother's four-bedroom bungalow in Armacao De Pera included playing puzzles, swimming and relaxing.

The inquest, sitting at Eastbourne Magistrates' Court, heard that the adults trusted the children to obey their instructions not to go into the 10m-long oval pool without adult supervision.

In the time that Ms Gardner and Rupert's father, accountant Adrian Marshall, were in the property's office looking at an online map, Rupert drowned.

Explaining the moments leading up to the tragic discovery, Ms Gardner said: "I just remember thinking I better go outside. I just felt it was time to move outside.

"I went down to the pool and I saw (Rupert) at the shallow end. He was lying flat, face down in the water. He was wearing a towel and leggings.

"I ran in, pulled him out, and started breathing into him. I yelled." Ms Gardner explained she had recently completed a swimming teacher's course.

Despite efforts to resuscitate him, a Portuguese pathologist later ruled that Rupert, of Heron's Ghyll, Uckfield, died from "asphyxia as a result of drowning".

Mr Marshall said that out of all three children Rupert was least interested in swimming and generally had to be "coaxed" into the water.

He told the inquest how they implored Rupert to "come on, come on" as resuscitation efforts were made by the pool, which was more than two metres deep at its deepest.

Mr Marshall said it was a mystery why Rupert had entered the water. There was speculation that he may have been looking for a stray ginger Tom cat seen recently at the bungalow.

Rupert's mother, Sophie Marshall, told the hearing that Rupert was extremely long-sighted and she had been worried about the proximity of the pool.

East Sussex coroner Alan Craze, recording an accidental conclusion, said he had sympathy for everyone involved in the tragedy.

He added he did not know what was worse - for the people who were there when Rupert drowned or for his mother who was not.

"Nobody is going to forget this, nobody pretends they are ever going to forget this," Mr Craze said in his closing remarks.

"But my hope is that with the benefit of the passage of time, each parent will be able to move on."