The two-year-old son of a Bronx man saw himself shot when the shooter got involved in an argument with the child’s mother.

A 2-year-old boy watched as his father was gunned down on a Bronx street by a gunman who intervened in a fight between the child’s parents, heartbroken relatives said.

Marquis Lane, 31, had an argument with his ex-girlfriend, who is the mother of his son, near Park Avenue and E. 167th Street in Morrisania around 8:50 am Tuesday, according to police sources.

According to the police, a man who knows the mother intervened and shot Lane in the chest.

“The 2-year-old boy was there when it happened,” Lane’s grandmother Helen Hannibal said. “It was wrong. This should never have happened.”

Lane was rushed to Lincoln Hospital but could not be saved.

He was only a few blocks from the house he lived with his grandmother when he was shot.

“He was my grandson and I’m trying to accept what happened,” Hannibal, 75, said. “I loved him and will always love him.”

Lane worked in construction and was the father of four children.

“We’re all in shock,” Lane’s cousin Dionne Elliot said. We don’t know what the dispute was about.

Neither Hannibal nor Lane’s cousin knows the mother of his child, who disappeared after the shooting.

Police are still looking for the shooter. And Lane’s ex-girlfriend is considered a “person of interest” in the murder and is wanted for questioning, police said.

“I just haven’t come to terms with it yet,” Hannibal said, holding back tears.