An elderly man was struck and killed by a tractor trailer last night just outside Grand Central Terminal as rush-hour crowds looked on in horror.

The 77-year-old victim — whose name was withheld pending family notification — was crossing Lexington Avenue at East 42nd Street at around 7:15 p.m. as the truck made a right turn onto Lex.

The driver was unaware she’d hit anyone until witnesses flagged her down, cops said. She was not charged.

The victim was pronounced dead at Bellevue Hospital.