spotlight. >> reporter: david cassidy was the ultimate teenage ultimate, known as keith in the partridge family. his wide eyed charm captured the hearts of many girls worldwide. >> you're taking auto shop? me too! >> reporter: a musical sitcom about a family and a rock and roll band gave a national audience for his own music. ♪ i think i love you >> reporter: the show's first single topped the billboard 100 in 1970 and sold over 5 million copies. >> i was always a musician. i never pursued my career as a musician. it was just fate, the way the stars align themselves. >> reporter: cassidy's wispy voice broke out into sold-out arenas around the globe. his fan club had more members at one time than elvis or the beatles. in 1972 at the height of his