Keith Richards joins Eric Clapton onstage
Stones guitarist makes surprise appearance at Madison Square Garden.
The festival, which has been held every three years since 2004, is to raise money for Clapton's Crossroads Centre in Antigua, which treats substance abuse.
This marks the end of Clapton's month-long US tour in support of his latest album Old Sock.
You can watch a clip below of Keith Richards backstage at Madison:
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