Grady played cool older brother Robbie on 'Sons,' Singleton played Lucy's frenemy Carolyn Appleby.
Don Grady played the handsome Robbie Douglas on the '60s favorite.
The actor also was a Mouseketeer and an accomplished musician who scored the Blake Edwards comedy "Switch."
'My Three Sons' big brother Don Grady dies at 68. (AP) – 1 minute ago. THOUSAND OAKS, Calif. (AP) — Don Grady, who was one of television's most beloved big brothers as Robbie Douglas on the long-running 1960s hit "My Three Sons," died Wednesday.
Don Grady, star of the popular and long-running sitcom My Three Sons, has died. He was 68.