A young couple found dead in their Quebec apartment with an unharmed toddler last winter died as a result of a fentanyl overdose, the coroner confirmed.

The dangerous opioid fentanyl killed a young couple found dead in their Quebec apartment with an unharmed toddler last winter, according to a coroner’s report released on Thursday.

The bodies of Amelie Gauthier-Matte, 20, and Christopher Lecouvie, 32, were discovered in an apartment located at 73 Rue Begin in Gatineau, Que. on Feb. 27. Their bodies were found in an advanced state of decomposition intertwined on a bed.

It’s believed the couple had died four days earlier.

Lecouvie’s three-year-old son was also found safe inside of the apartment after surviving for four days on his own.

Gauthier-Matte and Levouvie’s bodies were only located because a neighbour noticed the toddler throwing toys out of a window and checked in on him, the coroner’s report said.

The couple died of respiratory failure caused by fentanyl intoxication, the coroner concluded.

In addition to the fatal dose of fentanyl, both Gauthier-Matte and Levouvie had MDMA and methamphetamine present in their systems, a toxicology test found.

Heroin was also discovered in Gauthier-Matte’s system and Levouvie had cannabis present in his body. Despite the other drugs present, the coroner report said it was the lethal amount of fentanyl that killed the couple.

Originally from northern Ontario, Gauthier-Matte had been living in Gatineau since October 2016 to attend school.

With files from CTV Ottawa