As first reported in last night's Evening Times, Evan Mohammed was trapped as flames consumed the four-bedroom property in Kilmarnock, Ayrshire, shortly after 3am yesterday.
A major probe is now under way into the fire, from which two other children were rescued.
It is understood his mother, Sheree McGill, 34, had tried to rescue her children, but was beaten back by thick smoke and 1000ºF heat.
Evan's sisters, Yasmin, four, and three-year-old Nya, three, have now been released from hospital after being treated for smoke inhalation. Another daughter, Talia, 15, managed to save herself from the blaze.
Relatives said Ms McGill, who managed to flee the house with her boyfriend as it was engulfed with smoke, has been left "inconsolable" by her son's death.
It is understood they had been sleeping on the ground floor of the two-storey house in Altonhill Avenue while the younger children were upstairs.
Firefighters called to the property carried the two girls and Evan to ambulances outside, battling "intense heat and thick acrid smoke". They were taken to Crosshouse Hospital in Kilmarnock, where Evan was pronounced dead.
Local newsagent Mohammed Anwar, 46, said: "The little boy and his sisters were always in my shop. He was a lovely boy. It's so sad."