His new wife, whom he married earlier that year, was tickling the ivories and playing famed composer Ludwig Van Beethoven when he had a brilliant idea.
Lennon recalled: “Yoko was playing Moonlight Sonata on the piano. She was classically trained. I said: ‘Can you play those chords backwards?’ and wrote Because around them.”
After reversing the chords and melodies of Midnight Sonata, Lennon created a brand new composition for the track, creating the choral track that became Because.
READ MORE: The Beatles: Lennon treated people ‘incredibly different’ to McCartney
Creating the music for the song was a particularly involved process for the band as well.
Producer George Martin revealed years later how he used a Moog synthesiser on Because.
This is one of the only Beatles tracks to include the instrument.
“Each note between the guitar and harpsichord had to be exactly together, and as I’m not the world’s greatest player in terms of timing, I would make more mistakes than John did.
“So we had Ringo playing a regular beat on hi-hat to us through our headphones.”