A young man is dead after a threesome turned suddenly violent early Monday morning.

According to the Daily News, a 20-year-old man was stabbed in the back and chest and claimed to have been hit in the head with a bat when he banged on an apartment door in the upscale Brooklyn neighborhood of Park Slope, begging for help — but also pleading with the apartment resident not to call 911.

He collapsed soon after, and was pronounced dead at a nearby hospital.

The precise circumstances that led to the murder remain unclear in this developing story, and none of those involved have been identified.

READ UPDATE: Suspect in threesome murder believed victim raped his girlfrend

The Daily News reports that the victim came to the Park Slope building for a group sex encounter with a 21-year-old man and a 21-year-old woman.

The woman became upset when one of the men started filming the encounter, and the 21-year-old man, who lives in the apartment where the threesome took place, then drove the woman back to her home on Staten Island.

The woman reportedly told her boyfriend, who did not participate in the group sex, that she had been raped, but police told the Daily News there were no signs the sex was nonconsensual. The victim had a girlfriend who arrived to the scene Monday morning. She also did not participate in the group sex.

The victim remained at the apartment while the man drove the woman home, and the victim decided to leave after the man came home. Surveillance cameras reportedly recorded three men chasing him as he tried to get out the building. He then banged on an apartment door.

A relative of the woman who answered the door spoke to the Daily News:

“He fell into her house, she opened the door … he was apologizing, ‘I’m so sorry. I’m so sorry,’” the relative said. “He says, ‘They hit me in the head, they hit my head with a bat.’ She said there was so much blood just gushing out of him.”

“He went to stand up, I don’t know if he was gonna try and leave or what, (and) collapsed on the floor,” she continued. “She said his whole body started jerking and then they came, he barely had a pulse.”

At some point during the course of events, the victim’s girlfriend reportedly received an ominous message via Instagram:

“Your boyfriend f****ed up and will be taken care of.”

The woman arrived to the scene a few hours after the murder, and was extremely distraught.

“(Why) didn’t you go home? Why didn’t you listen to me?” she reportedly said. “He better go to f****ng jail! (Will) you guys get him please? … My baby, my baby, I love you so much.”

This is a developing story and will be updated as more information becomes available.