A Bronx mom who simply went to answer the doorbell over the holiday weekend was fatally shot through the peephole in a “street justice” hit tied to her gangbanger son, sources said Sunday.

Wendy Martinez, a 45-year-old hospital receptionist, was in her Concourse Village apartment with her 14-year-old son Saturday when the doorbell rang around 9:45 p.m., police sources said.

Her elder son, a suspected gangbanger who was due to appear in court Monday for a 2014 fatal shooting, was not in the apartment at the time.

Martinez asked who it was but got no reply, according to sources.

She asked again after a second ring, and then slid open the peephole when she heard no response. That’s when the gunman pumped a single, fatal shot through the viewing slot that struck Martinez’s face.

There was surveillance video of the killer at the building — but he carried an open umbrella to shield his identity, sources said.

The killer fled and Martinez’s teenage son hid in a bedroom and called 911, sources said. He was so shocked and frightened that he had to be coaxed out of hiding when investigators arrived.

Cops believe the cold-blooded killing is connected to Martinez’s older son, Brian Solano, 25, who faces murder charges in the Dec. 8, 2014, shooting death of 21-year-old Willie Lora.

Solano is a reputed Trinitarios gang member, according to police sources, who say the mom’s apartment may have been targeted by the rival Bloods offshoot The Eden Boys.

Solano was on Long Island with his girlfriend when his mother was shot, police sources said.

“That’s a gang-related hit,” a source said of Martinez’s murder. “This is street justice.”

Solano had a court hearing in his slay case scheduled for Monday, but law enforcement sources said both the defense and the prosecution now are seeking an adjournment following the mother’s grisly slaying.

Gangbangers had made threats against Solano on Facebook right after Lora’s murder but none recently, sources said.

Solano spent nearly three years on Rikers Island awaiting trial in the 2014 case but was released on his own recognizance late last year after a private investigator got a pair of grand jury witnesses to say their testimony was coerced by law enforcement.

The PI, Manuel Gomez, said of Saturday’s shooting, “The target was toward the older son, Brian.”

Solano’s lawyer, Dawn Florio, did not return messages seeking comment.

Police removed the entire peephole as evidence Sunday, and a bloody towel could be seen on the floor inside the apartment.

Meris Valdez, a nurse who worked with Martinez at Lincoln Hospital, said she was a dedicated mother. “She loved her sons. She would do anything for her sons,” Valdez said.

Neighbor Hector Flores, 54, added, “This is a safe building. No drugs, no people hanging out on the corners. To hear the gunshot and find out something like this happened here, it’s shocking.”

Additional reporting by Kevin Sheehan and Joe Marino