A man was fatally shot by his beau’s ex during an argument in Staten Island early Sunday, cops said.

The victim, believed to be in his 30s, got into a fight with his girlfriend’s former flame about the woman’s child while in front of a house on Bement Avenue in Port Richmond at around 3 a.m., sources said.

The ex then shot the man in the stomach before fleeing, cops said.

The victim was taken to Richmond University Medical center, where he died an hour later, cops said.

There have been no arrests.