The Laurel County coroner said a 2 1/2-year-old boy died Friday after being left in the back seat of a vehicle while his grandmother went to work.

The boy was found dead inside the SUV at 4:45 EDT, according to Douglas Bowling, the Laurel County coroner.

Bowling said the child died of hyperthermia.

The boy had been in the vehicle with the windows rolled up "probably around eight hours," Bowling said. His grandmother found him when she returned to her car after work, he said.

Bowling said it had not yet been determined how hot it was inside the vehicle. The high temperature in London on Friday was 76, according to the National Weather Service.

He said the incident was under investigation by police.

A call to London police was not immediately returned.