A 50-year-old man flipped out and killed his girlfriend and two other men after walking in on them having a threesome at her Brooklyn apartment, police said.

Hours later, the jilted lover admitted to cops he was so furious that he carved up the two mens’ bodies and dumped them somewhere in New Jersey.

“He made statements implicating himself in the deaths,” said NYPD spokesman Paul Browne, regarding the triple homicide at 1518 Eastern Parkway in Brownsville.

It is unclear whether three victims were shot or beaten to death.

The suspect spotted his 51-year-old girlfriend having sex with the two men shortly after midnight and left a voicemail with a friend saying he killed the three of them, cops said.

The message, was passed on to cops, led them to the woman’s first floor pad about 2 p.m. The suspect was found hovering over her dead body in a back bedroom.

He admitted to the murders and was taken to the 73rd Precinct in Brownsville for questioning.

Regine Nole, a 46-year-old home attendant who lives across the street from the murder scene, said the suspect “didn’t look afraid or upset” when cops escorted him out of the building.

“He just put his head down and went into the police car,” Nole said.

Lulu Facey, 30, who lives in an apartment a floor above the murdered woman, said she heard a lot of screaming late last night and “someone yelling ‘Help! Help!’” But Facey did nothing and “went to sleep” because she thought the commotion was over dogs barking at another apartment.

Nole said she heard from neighbors that the woman was “beaten to death.”

“She was dating more than one guy and just moved into this apartment three weeks ago,” she said.

Additional reporting by John Doyle