Montreal police are investigating a possible double murder-suicide after a mother discovered the bodies of her two sons and her boyfriend in their Montreal apartment early Saturday morning.

Sylvie Breton, 33, called police to the family's Ville-Emard apartment block at 1:40 a.m.

"Everything is pointing out to a double homicide followed by a suicide that was committed by the 72-year-old gentleman that was found on the scene," Montreal police Const. Yannick Ouimet told reporters at the scene.

"At this point, investigators still have to meet with some witnesses to confirm the hypothesis."

Police suspect strangulation in the deaths, though autopsies will likely take place Monday or Tuesday to confirm what caused the deaths of the two boys, seven-year-old Anthony and one-year-old Gabriel, and their father Jacques Tanguay.

Breton was taken to hospital where she was treated for shock and released. She has been ruled out as a suspect and is now considered an important witness in the case.

Police suspect Tanguay strangled the boys before taking his own life.

Relatives say they never imagined Tanguay, a retired pizza delivery man, could do something like this.

"If he had to kill him(self) fine, but why he have to touch the kids," the boys' grandfather Roger Breton told CTV News.

But the police believe Tanguay was likely distraught at the prospect of a relationship falling apart.

"This is a tragedy that took place, a father that was maybe feeling lonely, or feeling like the relationship was going away, and decided to take the lives of both of his kids," Ouimet said.

The couple had been together 13 years.

With files from CTV's Rob Lurie in Montreal and The Canadian Press