A spokeswoman for the New York City medical examiner's office has identified the man as Dennis Shields.
The 51-year-old Shields had been known for being the on-again, off-again boyfriend of Frankel, who gained fame as a star of "The Real Housewives of New York City."
Police responding to a 911 call say they discovered the body shortly after 9 a.m. on Friday at President Donald Trump's high-rise on Fifth Avenue.
An emergency medical service team pronounced Shields dead at the scene.
Frankel went to high school with Shield's estranged wife.
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