Mikaeel Kular's body was discovered on woodland behind a house at Kirkcaldy in the UK in mid-January.
His mother Rosdeep Kular had reported him missing the day before from their home in north Edinburgh.
The 33-year-old woman has since been charged with his murder.
The discovery of Mikaeel's body followed a major investigation and an extensive day-and-night search in north Edinburgh involving police and hundreds of local people and volunteers.
Members of the public also made more than 500 calls to a dedicated phone line set up in the wake of Mikaeel's disappearance.
Mikaeel's death certificate has been released by a registrar in Kirkcaldy.
It lists the cause of death as "peritonitis and infra-abdominal haemorrhage" (pending investigation).
Peritonitis is the inflammation of the peritoneum, the lining of the abdomen.