Paul McCartney made a guest appearance with Steven Van Zandt’s band in London to complete what the Bruce Springsteen guitarist called “unfinished business.”
It's almost universally regarded as a classic today, but in many ways, the Beatles' Sgt. Pepper's Lonely Hearts Club Band was an album decidedly ahead of its time.
"Wonderful Christmastime" is Paul McCartney's contribution to the Christmas genre. In my opinion, not his best effort, but hey, it's bloody Paul McCartney, so I'll shut up.