Police are investigating the fatal stabbing of an Upper East Side man in his apartment Monday evening, police said.

Police went to the fifth-floor apartment on East 85th Street after receiving a 911 call of an unconscious man at about 6:49 p.m.

Hector Rossy, 53, was pronounced dead at the scene, police said.

He was identified as Hector Rossy, according to police.

The investigation is ongoing, and the medical examiner will determine the cause of death.