Things may have been a little tense between Paul McCartney and John Lennon, but their final ever verbal exchange went on to inspire these two fan-favorite Beatles hits.

Carl Perkins wrote a song from the heart that inadvertently helped Paul McCartney process John Lennon's death.

“ ‘Yesterday’ feels like a shift in the balance of power,” says Leslie. “From the beginning they were equals, and ‘Yesterday’ wasn’t only just a hit, but the song that more artists covered than any other Beatles song. Paul even sang it onstage by himself when they performed. And it triggered John’s insecurities.”