You don't have to be a dyed in the wool Beatles fanatic to know that the sessions that produced Let It Be, the final album the group released (but not the last that they recorded!) were far from harmonious.
Envisioned initially by McCartney as a way of getting The Beatles back to their roots - recording live as a quartet with no studio effects and few overdubs - Let It Be proved to be just as much a wellspring of intra-band tension as the band's previous offering, The White Album, had been.
The internal strife finally boiled over on January 10, 1969, just eight days into the sessions for the album. After feuding with McCartney over how to play a lead break on “I’ve Got a Feeling,” Harrison walked out of the sessions, leaving The Beatles without a lead guitarist. Which is precisely how John Lennon, rather than George Harrison, ended up taking the solo to what became the album's lead single, "Get Back."
Why does this matter, you might ask? Well, as Cheatsheet pointed out, "Get Back" was one of only three McCartney-led tracks on which Lennon ever soloed, the other two being "Honey Pie" and "The End" (which featured solos from all four Beatles). It was also the band's only chart-topping American hit to feature a solo from Lennon.
Though Harrison would return to the fold days later, Lennon would again take the solo himself during the band's famed rooftop concert on January 30, 1969.
Sadly, no officially sanctioned footage of any of the group's multiple rooftop "Get Back" performances currently exist on YouTube. However, you can watch a high-quality edit of their rooftop performance of Lennon's stinging confessional, "Don't Let Me Down," below.