Police told how the off-duty medic was in the Caledonian forest reserve in Glen Orchy, Argyll, when Arran Cooper get into difficulties.
The youngster, from Rutherglen, Lanarkshire, had fallen into the River Orchy while on a camping holiday with his family.
The boy's father swam out to rescue the boy, the second eldest of four children, while his mother raised the alarm after reportedly seeing him face down in the water. As Mr Cooper pulled Arran on to the river bank, the boy's mother - who was on the other side of the river where the family were setting up a campsite - flagged down a passing car with a doctor on board.
It is understood the doctor - who was also on holiday - got out, jumped into the water and swam across the river to attend to Arran.
A major rescue operation was launched in the area, which included a coastguard rescue team and forest rangers, at about lunchtime on Tuesday.
An RAF Sea King rescue helicopter flew Arran to the Southern General Hospital, in Glasgow. He was later transferred to Yorkhill Hospital, but died in the early hours of yesterday morning.
His family, including his three siblings, have been left "devastated and distraught" by the tragedy.
It is not known how long Arran was in the water.
Glen Orchy is a popular spot with tourists and families having picnics.
The recent hot weather meant it would have been busier than usual.
The area is also popular with cyclists and has its own forest and mountain bike trail.
A police spokeswoman said: "At 1.45pm, a 10-year-old boy fell into the River Orchy near to Allt Broighleachan in the Caledonian forest reserve.
"He was rescued from the water and flown to Glasgow for treatment.
"He died in the early hours of Wednesday.
"A report will be submitted to the procurator fiscal."