It happened at about 5 a.m. at the County House Diner on Fulton Street in the Clinton Hill section.
Witnesses say a man was sitting at a counter with a woman when another man pulled out a gun and shot him in the abdomen.
The 34-year old victim was taken to Brooklyn Hospital, where he was pronounced dead.
His identity has not yet been released.
The suspect was taken into custody at the scene.
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