An autistic teen suffered a broken nose when he was robbed by a trio of strangers in the Bronx, police and law enforcement sources said.

The 19-year-old let the trio into the lobby of his apartment building on Jesup Avenue and West 172nd Street in Highbridge shortly before 4 p.m. on Wednesday, cops said late Friday.

But once inside, the three men turned on him — repeatedly kicking and punching the man until he fell to the ground. They stole his backpack and fled. It wasn’t immediately clear what, if anything, prompted the attack.

Video shows a female accomplice holding the door as the male suspects came and went. She then left the building with the others, including one man who can be seen in the video holding the dark-colored backpack.

The victim was taken to a nearby hospital for his facial injuries.

Police are still looking for the four suspects.