A 9/11 victim’s DNA helped police identify remains — found more than 20 years ago under a famed New York City address — as those of a teen last seen in 1969, authorities said.

Construction workers made the gruesome discovery on Feb. 10 2003 at 301 W. 46th St. in Manhattan’s Hell’s Kitchen neighborhood, where the famed rock night club “Steve Paul’s The Scene” once played host to some of music’s biggest acts.

“They were knocking through the concrete floor (and) a skull rolled out,” NYPD…