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 June 27. He was 68.

His “My Three Sons” co-star Barry Livingston, who played youngest brother Ernie, confirmed the death to the Associated Press. Livingston said that Mr. Grady had been suffering from cancer and was receiving hospice care at his home in Thousand Oaks, Calif., but the exact cause and place of death were not immediately clear.

Born Don Louis Agrati on June 8, 1944, in San Diego, Mr. Grady had a brief stint singing and dancing on “The Mickey Mouse Club,” beginning at age 13.

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

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

In the show’s earlier years, Mr. Grady was the middle brother, with Tim Considine playing the oldest, Mike, and Stanley Livingston playing the youngest brother, Chip. When Considine left the show, Barry Livingston became the adopted “third” son, and Mr. Grady became the cool, handsome and assured eldest brother.

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

A musical prodigy from a young age, Mr. Grady appeared with a band, the Greefs, in the series, and he played drums for the Yellow Balloon, a group that had a minor hit with a self-titled song in 1967.

He made a handful of guest appearances on TV series in the 1970s and 1980s but worked primarily as a musician and composer. Mr. Grady wrote the theme for “The Phil Donahue Show” and music for the Blake Edwards movie “Switch” and the popular Las Vegas show “EFX,” a showcase for “Phantom of the Opera” star Michael Crawford.

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