A Virginia teenager who authorities said intervened when his mother was being attacked by her boyfriend — fatally shooting the man — has been charged with second-degree murder.

Police said the son, who is 15, shot and killed John Conroy Jr., 37, as Conroy physically attacked his mother during an argument at their house.

The teen faces charges of second-degree murder and use of a firearm during the commission of a felony, Deputy Commonwealth’s Attorney Duncan Minton said. The teenager’s name is not being released because he is charged as a juvenile.

Minton said every homicide in Virginia is “presumed to be murder in the second degree,” but that the charge can be reduced or increased as the investigation goes on.

“Because of the fact that he’s a juvenile and because there may be extenuating circumstances, there is a whole wide range of things that could happen,” Minton said.

The teen will appear for a hearing in Spotsylvania juvenile court within the next 21 days, Minton said.

Police on the afternoon of March 8 responded to a report of a shooting at a house in the 5300 block of Towles Mill Road. They said they found Conroy dead in the front room with multiple gunshot wounds.

An argument had broken out between Conroy and the mother, 36, and at some point Conroy attacked her, authorities said.

The teen took a semiautomatic gun that was in the room and fired at Conroy, striking him several times, according to a statement from the Spotsylvania County Sheriff’s Office.

The teen’s mother was treated for injuries that weren’t considered life-threatening, the statement said. Police took the teen to Rappahannock Regional Juvenile Detention Center.