A Brooklyn man was sucker-punched on the boardwalk in Brighton Beach and died the next day — but not before telling cops he had no clue who slugged him or why, according to police and sources.

Dimitry Goldfarb, 52 — a longtime local known to neighbors for his love of pop music — managed to tell cops about the July 9 attack from his hospital bed, sources said.

“It was a complete stranger to him,” a source told The Post. “He didn’t know who he was. Did not know why he was assaulted.”

Now the NYPD is on the hunt for a brawny man suspected of carrying out the assault.

Cops on Friday released surveillance stills of a shirtless man in his 30s shown calmly walking north on Brighton Sixth Street with a woman.

They believe the guy punched Goldfarb at the corner of Riegelman Boardwalk East and Brighton Sixth Street around 5:45 p.m. before fleeing with the gal pal.

Police responding to a 911 call about the assault found Goldfarb at the site with a severe head injury.

He was taken to NYU Langone Hospital-Brooklyn and later transferred to Bellevue Medical Center, where he was pronounced dead after undergoing surgery.

At a press conference on Friday, NYPD Chief of Detectives Dermot Shea said the fight could have been sparked by something “as simple as a conversation.”

“We’re not exactly sure what started this fight, but we do have an individual that was beaten up pretty badly and unfortunately caused his demise,” said Shea.

“We’re very confident somebody in that neighborhood will come forward.”

Neighbors described Goldfarb as a fixture in the neighborhood with an affinity for retro pop music — including ABBA and Russian pop — and a regular at Tatiana Grill, a popular boardwalk hot spot located around the corner from his apartment.

His nickname was “Patlatiy,” which translates to “shaggy,” they said.

“He listened to music, ‘80s pop. Loud. He drank beer at Tatiana,” said Andrey Semyonov, the superintendent of Goldfarb’s building. “He lived here a long time.”

Another neighbor said Goldfarb typically “kept to himself.”

“I did have a soft spot for him because he used to wear a Ukraine Dynamo [soccer team] jersey,” said the neighbor, who is from Ukraine.

Goldfarb’s alleged attacker is believed to be 6 feet tall, 220 pounds and in his 30s, with long brown hair, police said.

In the surveillance footage, the shirtless man had a white cloth tucked into his shorts and is accompanied by a woman with a red top and black shorts.

Anyone with information is asked to call NYPD’s Crime Stoppers hotline at 1-800-577-TIPS (8477) or 1-888-57-PISTA (74782) for Spanish.