March 15, 1973.
3 seconds sound clip from the Back to the Future Part II movie soundboard.
You can hear this line at 00:51:06.787 in the Blu-ray version of the movie.
Quote context
[...]
- Oh, they must have hit you over the head hard this time.
- Mom, I just want to know one thing. Where's my father? Where's George McFly?
- Marty, George, your father is in the same place he's been for the past 12 years: Oak Park Cemetery.
- No. No! This can't be happening!
- No! Please, God, no! No, please, God. Please, God, no. This can't be happening. This can't be...
- I'm afraid it is happening, Marty. All of it.
- When I learned about your father, I figured you'd come here.
- Then you know what happened to him? Do you know what happened March 15, 1973?
[...]