The son of legendary TV newsman Ted Koppel was found dead in a Washington Heights apartment under mysterious circumstances Monday morning after a daylong drinking binge with a man he had just met in a Midtown bar, law-enforcement sources told the New York Post.

Andrew Koppel, 40, of Rockaway Park, Queens, was declared dead at around 1:30 a.m. after paramedics were called to the rundown apartment in what a law-enforcement source called a "s- - - building" on 180th Street at Audubon Avenue, where he had been found unconscious and not breathing in a bedroom, the sources said.

Koppel -- who was an attorney for the city Housing Authority -- was a slobbering mess when he was brought to the apartment at around 11 p.m. by Russell Wimberly, a 32-year-old waiter he had met at a Hell's Kitchen bar nearly 12 hours earlier.

Koppel "was just really messed up when he came in. He was very drunk," said Belinda Caban, 53, who lives at the apartment.

Caban, who called Wimberly a drinking buddy, told The Post: "I didn't understand anything [Koppel] said. We took him to the bedroom and laid him down to rest."

After a couple of hours, she and Wimberly discovered he had urinated and defecated in the bed and appeared not to be breathing. They called 911.