A tragic scene unfolded in a Queens apartment building as a 75-year-old retired educator was discovered dead, his throat slashed, in what authorities and residents describe as a violent rampage by a neighbor.

Police arrived at George Dournadounas’s Astoria residence on 33rd Street around 1:40 p.m. after receiving a report of a slashing incident. Upon arrival, officers found Dournadounas with a critical neck injury, as confirmed by the NYPD.

Tragically, he succumbed to his injuries before any medical intervention could be provided.

Residents were shocked by the news, with one neighbor revealing that the former high school math teacher was allegedly killed by a “mentally ill” tenant with whom he had ongoing disputes.

“He returned home today, and apparently the neighbor he had conflicts with attacked and killed him,” Ray shared with The Post on Tuesday evening. “It’s unbelievable. They didn’t see eye to eye, but George was a kind individual who never troubled anyone. He came home, and this tragedy happened.”

“George was a gentle and amiable man. This neighbor harbored a dislike for him, but George never provoked him,” Ray continued.

The local added the alleged killer — described as a burly, 30-something who lives with his mother — often harassed the victim, mocking his Greek heritage and hurling expletives at him.

Ray said he was asleep when the deadly rampage erupted — waking only to screams as police arrived to the building.

He said Dourndounas, who lived across the hall, had earned his PhD about two years ago and was planning to return to the classroom as a college professor.

Police have not released any details about arrests made, potential foul play or what led to the fatal encounter.

The investigation is ongoing.