Last fall, DAVID CASSIDY dared DANNY BONADUCE... who played his younger brother on "The Partridge Family"... to learn one of the Partridge Family songs, and perform it with him.  And it actually happened on Saturday night in Atlantic City.

They performed "Doesn't Somebody Want to Be Wanted"(Here's Video.)

Before beginning, Danny asked the crowd, quote, "You want to see something nobody has ever seen before?  Me, plugging in a bass guitar!"  (Danny pretended to play the bass and lip-synched on the show.  David sang for real.)