A suspect has been arrested for gunning down a 31-year-old man inside an illegal after-hours Brooklyn bar.

Gabriel Hernandez, 27, is facing manslaughter and weapon possession charges for allegedly shooting Giovanni Rivera in the back and chest inside the unlicensed spot on 50th St. near Third Ave. in Sunset Park about 5 a.m. Monday.

Medics rushed Rivera to NYU Langone Hospital-Brooklyn, where he died. He lived in Borough Park, according to cops.

Hernandez was nabbed at the scene and charged a few hours later. His arraignment in Brooklyn Criminal Court was pending Wednesday.

“ We don’t really know much, so it’s very hard to cope with it,” Rivera’s sister, Maria Hernandez, told the Gothamist Tuesday. Rivera worked in construction and enjoyed customizing cars, she said.

He was saving up money to visit his mother in Mexico, Hernandez added.

“He was a very kind, very good-hearted person,” she told Gothamist. “He wasn’t looking for any trouble.”

The suspect has a criminal record that includes six arrests, mostly for assault and weapons possession. He was most recently arrested on misdemeanor assault charges for punching a 28-year-old relative on Oct. 17.

He was released without bail on the misdemeanor assault charge and recommended he take part in an alternative to incarceration program that focused on problem solving and anger management, according to court documents.

On May 25, cops busted the suspect for gun possession when he was pulled over riding a gas-powered moped in Sunset Park and tried to run off when cops learned he had a suspended license, police said.

When officers caught up with him, they found a pistol in his waistband.

He was ordered held on $20,000 bail which he paid and was released, officials said. Both this case and the misdemeanor assault case are still pending in court.

Rivera, cops said, also had six arrests under his belt and was arrested on July 13 for allegedly attacking his former girlfriend and robbing her of her cellphone. He was released at his arraignment since the charges were not bail eligible, officials said.

That case was still pending in Brooklyn Criminal Court when he was slain.