His father and 4 year old sibling remain in hospital.
Police are investigating a caravan fire which broke out in Ceredigion - killing a three year old boy.
Zac died and his brother Harley, four, is in a critical condition following the blaze on Sunday morning.
Shaun Harvey, 28, the boys' father, is in a stable condition in hospital after escaping the fire with the eldest boy.
It happened in the village of Ffair Rhos near Tregaron on Sunday morning.
Detective Chief Superintendent Steve Cockwell said: "We received a call at 5.35am today (Sunday, January 19), reporting a fire at a caravan at Ffair Rhos.
"Enquiries so far lead us to believe that three people were inside the caravan at the time the fire broke out. These were a father and two children – a four-year-old, and a little boy who we believe to have been aged three.
"While the father and the eldest child were able to get out of the caravan, the younger of the siblings was tragically found deceased inside.
"Our thoughts are with his family at this extremely difficult and traumatic time, and specialist officers have been put in place to support them.
"The father is currently in a stable condition in hospital, while the four-year-old is critical but stable. Both suffered burns.
"The Criminal Investigation Department is investigating the cause of the fire, and a major incident room has been set up at Aberystwyth Police Station.
"We are also working closely with Mid and West Wales Fire and Rescue Service, who were in attendance when our officers arrived. We would like to thank our colleagues at the fire service for their professionalism in dealing with what turned out to be a highly traumatic incident.
"We would like to speak to anyone who was in the Ffair Rhos area around the time of the fire, who might have information that could help our investigation.
"This was a tragic incident, and we will be doing all we can to find answers for the family, whose world will have been torn apart by this morning's events."
If you have any information that could help officers, call the Criminal Investigation Department on 101, using Storm reference 39 of January 19.