Tito Jackson, brother of the late Michael Jackson and co-founder of the Jackson 5, has died. He was 70 years old.

His family made the stunning announcement Sunday.

“It’s with heavy hearts that we announce that our beloved father, Rock & Roll Hall of Famer Tito Jackson is no longer with us,” Tito’s sons TJ, Taj and Taryll said in a statement on Instagram. “We are shocked, saddened and heartbroken.”

While an official cause of death has yet to be determined, Steve Manning, former Jackson family manager, told Entertainment Tonight, he believed the pop icon died of a heart attack while driving from New Mexico to Oklahoma on Sunday.

Tito, born Toriano Adaryll “Tito” Jackson in October 1953 and the third of 10 children, was the least-heard member of the Jackson 5 as he was a backup singer and played guitar for the group, while his brothers Jackie, Tito, Jermaine, Marlon, and Michael were more prominently featured.