A 3-year-old boy who died over the weekend in an apartment fire in Grand Crossing had been left in the apartment by an adult who escaped and didn’t realize the boy was there, according to the Illinois Department of Children and Family Services.

Maqkwone Jones was pronounced dead at 11:36 a.m. Sunday at Comer Children’s Hospital, according to authorities.

The boy and three siblings had been staying there with their foster mother, a female relative, according to DCFS. They had been placed with the relative in September 2017 after a DCFS investigation of their birth mother for child abuse and neglect.

Those other siblings — ages 2, 8 and 9 — were not in the apartment at the time of the fire and have since been placed in other foster homes for the time being, according to DCFS.

The foster mother was not there when the fire started, according to Neil Skene, a spokesman for DCFS. An adult friend was sleeping in the apartment, but did not realize the child had been in the apartment until she escaped and called the foster mother to let her know about the fire.

Fire crews arrived about 10:30 a.m. Sunday at 1421 E. 67th Pl., and were told the boy was upstairs and then forced their way into the locked apartment to get Maqkwone, fire officials said. Chicago Fire Department spokesman Larry Langford said the boy was in cardiac arrest, a common result of heavy smoke inhalation.

The death is under investigation by the Illinois Department of Children and Family Services and the Chicago Police Department. Maqkwone’s official cause of death is still pending, according to the Cook County Medical Examiner’s office. Langford added that when it comes to smoke inhalation, every minute can make the difference between life and death.

A neighbor, Karen McClenden, said the fire ripped through the building in just 10 minutes. CFD found the fire suspicious enough to turn over investigation to the CPD. That investigation is still ongoing.