It was Eric Roy's family who first announced the death in a post on his Instagram.
According to the post, Roy was diagnosed with pancreatic cancer over three years ago but kept the disease out of the public eye.
Later on Wednesday, Brest also confirmed the death.
"Loved and respected by the supporters, he helped write the most beautiful pages in the club's history and enabled it to reach a historic level," the club wrote.
Roy enjoyed great success with French side Brest after taking over as coach in January 2023. A third-place finish in the league and appearing in the Champions League were the major highlights during his time at the club.
He was 58 years old.
