According to what I read about it, the song was one John had recorded at home but never released. When Paul found out about it, he and the other Beatles recorded it using the recording. This made a final Beatles recording possible. It makes me cry but in a happy way. Thank you, sister.
Starts about 8:50. Jim Croce's saddest song, "Operator", played for the last time. Only an hour later, his flight crashed into a tree and he was gone.