Paul McCartney - let it be live, 1990

"Let it Be was always Paul’s song, he wrote it and it was about his mother Paul was the lead singer, however, I did hear a rehearsal demo where John did sing the opening, more like playfully singing and it was John sort of helping Paul work out the construction of the song but it was always intended to be Paul as the lead singer, often times during rehearsal’s other Beatles members would sometimes playfully sing each other’s songs, either as a joke or in helping each other out as a team, but the final recording was all Paul and the others as back up vocals and instruments."