Police have arrested a suspect in the fatal stabbing and beating of a man involved in a Park Slope ménage à trois — and he’s the boyfriend of the woman involved in the threesome, authorities said.

Christopher Membreno, 24, was picked up Monday evening and charged with murdering 20-year-old Manos Ikonomidis.

Ikonomidis and pal Jack Doherty, 21, were involved in a consensual threesome with Membreno’s gal pal inside Doherty’s Brooklyn pad Monday, police said.

The woman became irate when she realized one of the men tried to film the steamy encounter, cops said.

Doherty drove the woman back to her Staten Island home, and she then contacted Membreno and told him she had been raped, police said.

The woman also sent a message through social media to Ikonomidis’ girlfriend which read: “Your boyfriend f–ked up and will be taken care of,” according to sources.

Membreno and two other men showed up at the building, where they found Ikonomidis in the lobby and stabbed him multiple times, cops said. They also bludgeoned him about the head with baseball bats, police said.

The mortally wounded Ikonomidis spent his last moments frantically banging on neighbors’ apartment doors begging for help, residents said. He later died at a local hospital.