A threesome s*x between two men and a girl has turned seriously bloody leaving one participant dead.

A threesome in Park Slope spiraled into a deadly attack with bats and knives after one of the participants began filming the s*xcapade, police have confirmed.

According to Daily News, the Brooklyn bloodshed left Manos Ikonomidis, 20, dead of three stab wounds in the chest and back.

He collapsed on the first floor of a building at 16th St. and Seventh Ave. just after 4 a.m. Monday.

Earlier, he’d been locked in a steamy romp with an unidentified woman and 21-year-old Jack Doherty.

“It’s something out of a horror movie,” stunned building resident Carol Petersen, 37, said. “It’s horrible. It’s a nightmare.”

Doherty was being questioned by police, but was not a suspect in the slaying, sources said.

Police sources said the ménage à trois in Doherty’s apartment came to a violent end when one of the guys started filming the tryst. The woman became irate. Doherty drove the woman — whose name was not available — back to her Staten Island home, leaving Ikonomidis alone, sources said.

A resident in the building said the woman contacted her boyfriend — who was not involved in the threesome — and alleged she’d been raped.

Ikonomidis’ girlfriend — who also was not involved in the s*x play — received an ominous Instagram message reading “your boyfriend f—-d up and will be taken care of,” sources said.

Police sources said cops had found no evidence the encounter was anything but consensual. Around the time Doherty returned to the apartment, three men arrived at the building.

They had revenge on their minds, sources said.

Surveillance cameras captured two white men and a black man chasing Ikonomidis with baseball bats as he tried to leave the building, sources said. Ikonomidis was beaten with bats and stabbed, the sources said.

Bleeding from his wounds, the victim knocked on the door of Joy Liguori’s nearby apartment and collapsed, leaving bloody handprints. He was taken away later in an ambulance before his girl friend arrived.

She said she did believe it was real.