United Kingdom, July 26 -- Billy Joel felt "really hurt" after Sir Elton John encouraged him to go to rehab.

The 76-year-old star admits that some "bad blood" developed between himself and Elton, after the Your Song hitmaker publicly suggested that Billy needed to spend some time in rehab.

In the HBO documentary Billy Joel: And So It Goes, he says: "Elton had made a comment that he thought I needed real rehab. He chalked it up to, 'Oh, he's a drunk.' And that really hurt me.

"I said wait a minute? Don't you know me better than that? And there was bad blood for a little while. There was a dovetailing of things that happened during that time."

Billy recalled feeling at "rock bottom" when he read Elton's comments.

He said: "I was disill...