A 39-year-old father was fatally shot at a Brooklyn baby shower Saturday morning by one of the men who beat up his son earlier in the night, police said.

Hilario Paulino Cortez-Vidals took a bullet to the head about 1:05 a.m. near the glass entrance of the Afrika House banquet hall on Bedford Avenue in Flatbush-Ditmas Park, cops said.

Cortez-Vidals was declared dead at Kings County Hospital.

Earlier in the evening, a group of Hispanic men assaulted the victim’s son, cops said.

The trio punched and kicked the 21-year-old in face and the fled the gathering.

But one of them returned a short time later and fired off one shot, which struck their rivals father in the head.

It’s unclear that he was the intended target, cops said.

Cops recovered a 9mm shell casing at the scene, police sources said.

Police are interviewing the other revelers to determine who fired the shot.