A 15-year-old boy was arrested in the brutal beating and robbery of a teen in Brooklyn, cops said Monday.

The teen was assaulted, knocked unconscious, and then robbed of his sneakers and jeans in Brownsville, cops said.

The 16-year-old victim was riding the L train around 3:30 p.m. Friday, cops said, when a group of five hooligans surrounded him inside the train at the Broadway Junction station and asked him, “What gang are you in?”

When he told them he wasn’t in a gang the teens began to punch and kick him in the face and body, cops said.

Once the victim was knocked unconscious they took his cell phone, sneakers and jeans before booking it out of the station, cops said.

The victim was taken to Brookdale Hospital with a concussion and severe injury to his right eye, cops said.

Brandon Parchment, 15, was spotted by two officers Sunday and charged with robbery.