No, it wasn't the day Sgt. Pepper taught the band to play. It was the day the band was officially torn apart forever. Hard to let Dec. 8th go by without noting this was the day John Lennon was shot to death outside the Dakota in New York City. 

Forty years! Sometimes, it seems like just a few minutes ago. 

Or as Paul McCartney might say, Yesterday. 

Paul McCartney, Ringo Starr And Yoko Ono Pay Tribute On 40th Anniversary Of Death