A man shouting homophobic slurs stabbed a gay man traveling with his boyfriend and his sister on a No. 1 train Saturday evening, according to the NYPD.

Police say the assailant got angry when he saw the victim, 28, with his partner, and argued with him as their northbound train pulled into 110th Street in Morningside Heights just after 7 p.m., cops said.

That’s when the attacker started yelling “you faggot!” at the victim.

He then stabbed the victim in the left side of the chest and fled, authorities said.

Emergency responders rushed the man to Mt. Sinai St. Luke’s Hospital, where he remains in serious but stable condition.

The stabber was still at large Saturday night and is described as a male Hispanic, about 6’1″ wearing a white shirt and khaki shorts.

The NYPD  is investigating this violent attack as a hate crime.