Grady played big brother Robbie Douglas on the show. Grady's death was confirmed by the actor's co-star Barry Livingston, who played the youngest brother in the series.
According to the Washington Post
, Grady had been battling cancer and was receiving hospice care at his Thousand Oaks, Calif., home. However, the place and exact cause of death were not immediately clear.
According to the Los Angeles Times
, Grady's musical talents helped him land an audition with "The Mickey Mouse Club," and he stayed on that show for several years. After leaving the Disney show he went to join the cast of "My Three Sons" when he was 16 years old.
According to the San Francisco Chronicle
, "My Three Sons" was one of the longest-running family sitcoms of all time with 380 episodes aired. Grady also made quite a few guest appearances on TV series throughout the 70s and 80s. He also wrote the theme for "The Phil Donahue Show," in addition to music for the film "Switch" and the Vegas stage show "EFX".
Livingston said that Grady would like to be remembered as a television icon as well as a teen idol—and for his amazing music.