A man killed outside a swanky Long Island yacht club realized he was in mortal danger just moments before his ex-girlfriend’s new beau stabbed him to death while she cheered him on, prosecutors said Tuesday.

Victim Christopher Millwater, 52, looked into the face of 32-year-old Victor Panebianco and said “you’re stabbing me?” before the maniac knifed him twice through his heart and lungs at a parking lot near Stony Brook Yacht Club on Nov. 10, Suffolk County prosecutors revealed in court.

Millwater then screamed for help as Panebianco sat on top of him and pushed the knife through his organs, officials said.

Millwater’s ex-girlfriend – 33-year-old Kacy Corso – witnessed the attack and had egged on her new boyfriend urging him “don’t believe him, don’t let him fool you,” prosecutors previously said.

Panebianco then allegedly kicked Millwater’s lifeless body in the head before he climbed back into his vehicle and fled the bloody scene.

The twisted couple drove back to North Carolina, where they shared an apartment, according to prosecutors.

They had driven to Long Island with plans to confront Millwater, who Corso said had continued to contact him despite her rebuffing his advances, officials said.

Panebianco was recently extradited back to Suffolk County and charged with murder, police said.

Both Corso and Panebianco pleaded not guilty and are due back in court Jan. 13 and 14, respectively.

“Today’s indictment reflects our unwavering commitment to seeking justice for victims of violent crime,” said Suffolk County District Attorney Ray Tierney.

Kacy Corso, 33, during her arraignment.

Millwater and Corso had been involved in a romantic relationship, but they eventually split, and she grew increasingly hostile toward him, officials have said.

Corso regularly slammed her ex in a series of nutty social media posts — warning him not to contact her and calling him a “grave robber.”

Corso had moved from New York to North Carolina, where she worked as a DoorDash and Uber driver, according to police.

But she plotted with her new boyfriend to drive back to Long Island, where they ambushed Millwater outside the yacht club that he was known to frequent, cops said.

Corso used her car to block the exit of the parking lot so Millwater couldn’t escape, according to officials.

He tried to maneuver his vehicle around her but that only set her off — and she rammed his car and disabled it, cops said.

Millwater made a run for it, but Panebianco jumped out of the passenger side of Corso’s car — chasing and tackling Millwater before he could get to safety, cops said.

Panebianco pressed Millwater about his past relationship and asked him if they were still an item as Corso egged on her unhinged boyfriend, prosecutors claimed.