Angela Castro, older sister to Fidel and Raul Castro, died on Wednesday at the age of 88.
She was surrounded by her children and was unconscious at the time of her death, Juanita Castro, her sister currently living in Miami, told the Associated Press.
Angelita, as she was called, was the oldest of the seven Castro siblings and long suffered from Alzheimer's disease.
She had been in a very delicate situation for some time, her younger sister added.
Her remains were taken from the Havana clinic where she was living, and her ashes were spread at the farm where she was born in the eastern part of the island nation.
Angela was the daughter of Spanish immigrant Angel Castro and Lina Ruz, his second wife.
Fidel Castro led the Cuban revolution in 1959 and ruled the country until he ceded power to his younger brother Raul in 2008. Raul has since worked to modernize Cuba's socialist economy.
Fidel, 85, was third born and Raul, 80, is the youngest Castro child. Both are known for their privacy in personal affairs, and rarely comment on family issues.
Angela's death has not yet been reported by Cuban state media.