Police in Gatineau are now investigating Wednesday's suspicious death as a murder.
Officers discovered a body at a home on Boulevard de la Cite-des-jeunes around noon on Wednesday.
They had been responding to a 911 call about an agitated man that was acting suspiciously.
The 21-year-old man remains in police custody as the investigation continues.
An autopsy is being conducted on the 83-year-old woman on Thursday morning.