OK, back to the 50's (barely!): This Bob Marcucci/Peter DeAngelis composition sung by Philly-native Frankie Avalon topped the charts during the last week of December of '59, making it the last #1 hit single of the 50's. It was his 2nd and last #1 hit. Donny Osmond's '72 cover peaked at #13. Song? First #1 hit?
Answer: "Why" by Frankie Avalon. His first #1 hit was "Venus" (NOT to be confused with Kevin Meaney's version!).