Billy Joel is opening up about a tough moment with longtime friend and tourmate Elton John. In the second part of the new two-part HBO Documentary, "Billy Joel: And So It Goes," the "New York State of Mind" singer shared how John's public comments that he needed rehab strained their friendship.

Billy Joel says there was once "bad blood" between him and Elton John. In the second part of a new two-part HBO documentary Billy Joel: And So It Goes, the "Piano Man" singer opens up about how the "Your Song" musician's public declaration that he needed rehab caused tension between them.