Elton John The Surprise Wedding Singer

John was a surprise guest as Laura Katzenberg got married to bigshot record producer Mark Sudack in Los Angeles this weekend.

It's not too surprising, considering Jeffrey Katzenberg was running Disney back when Elton did the soundtrack to "The Lion King" ... and the two have been friends ever since.

But the night before the Katzenberg bash ... John performed at ANOTHER huge wedding -- when actress Holly Valance tied the knot with U.K. billionaire Nick Candy at the Paramount lot in L.A.