THOUSAND OAKS, Calif. — 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.

His ‘‘My Three Sons’’ costar Barry Livingston, who played youngest brother Ernie, confirmed Mr. Grady’s death. Livingston said Mr. Grady had been suffering from cancer, but the exact cause and place of death were not clear.

‘‘It’s the oldest cliche in the world when TV brothers start referring to each other like biological brothers, but he was the oldest, and somebody I looked up to and learned from a great deal about life,’’ Livingston said.

Born in San Diego as Don Louis Agrati, Mr. Grady, 68, had a brief stint singing and dancing on ‘‘The Mickey Mouse Club,’’ starting at age 13.

But he was best known as one of Fred MacMurray’s ‘‘My Three Sons’’ on the series that ran from 1960 to 1972 on ABC and later CBS.

The popular show, which featured MacMurray as a widowed aeronautical engineer struggling to raise three boys, was among the longest-running family sitcoms of all time with 380 episodes.

In the show’s earlier years, Mr. Grady was actually the middle brother, with Tim Considine playing the oldest, Mike, and Stanley Livingston playing the youngest, Chip. When Considine departed, Barry Livingston became the adopted ‘‘third’’ son, and Mr. Grady became the cool, handsome, and assured eldest brother whom much of America adored.

He made a handful of guest appearances on TV series in the 1970s and 1980s, but he worked primarily as a musician and composer, writing the theme for ‘‘The Phil Donahue Show’’ and music for the Blake Edwards film ‘‘Switch.’’

‘‘The one real through-line in his life was music,’’ Livingston said. ‘‘I would think Don would love to be remembered for his great music as much as a teen idol and television icon.’’