The news seemed hard to believe, although many Cubans had for a long time feared it might be imminent.
Fidel Castro is ill - so ill that 13 days before his 80th birthday, he delegated all his powers to his brother Raul.
"We are very worried," Victor Gonzalez said, after he and his compatriots heard the announcement on television. "We are not used to being without him, he has led us for so long."
Uncertainty now marks a transition in which many Cubans expect to find weak points that allow for change.
Cubans usually say only "he" when they mean Fidel Castro. The last remaining true revolutionary from the 20th century has led the last communist state in the Western world for 47 years without interruptions.
Castro's rule: Key dates
Jan 1959: Appointed prime minister in February.
Late on Monday, Castro temporarily delegated power to Raul because he underwent surgery for intestinal bleeding, Cuban state television said, apparently reading from a hand-written note from the leader.
The problem was blamed on stress from overwork and travel during the past two weeks. Celebrations of his 80th birthday on August 13 were postponed until December.
Castro's life has been dominated by a deep-running dispute with the US, even beyond the demise of the former Soviet Union.
The small island nation in the Caribbean survived the collapse of the worldwide communist system led by Moscow, to which Castro had adhered.
The economic troubles that resulted from post-Soviet-era isolation left Cuba close to catastrophe in the 1990s.
Fidel Castro managed to survive this crisis, just as he had previously withstood conspiracies and assassination attempts and the corrosive effects of Washington's decades-long economic blockade.
In the current year, his 80th birth year, he appeared firm and uncontested at the head of the state.
But he also began to prepare Cuba, at home and abroad, for the period that is to follow his death.
A few weeks ago, Castro reformed the leadership of the Cuban Communist Party and put new people from the country's provinces in key positions.
The party must be, according to Castro, his real successor after the death of its leader.
Venezuela stepped in to fill the void left by the Soviet Union as the island's closest ally.
Castro went about building, together with the fifth-largest crude-oil exporter in the world, a Latin American front against the US.
Venezuelan President Hugo Chavez provides oil money, while Cuba provides human resources, in the services of well-trained doctors, teachers - and the guiding light of the dedicated revolutionary, now ill.
Castro was born August 13, 1926, in the East Cuban town of Biran, the son of a Spanish immigrant.
He attended a Jesuit school and studied law at the University of Havana. However, he did not go on to become a solicitor serving the poor country's small, wealthy elite but quite the opposite.
He became a revolutionary who undertook the political and social transformation of his country.
His first attempt was a failure. In 1953, Castro and his comrades stormed the Moncada Barracks in Santiago de Cuba, in an effort to trigger a popular uprising against dictator Fulgencio Batista.
Castro was condemned to 15 years in prison, but he received an amnesty after 22 months.
At the end of 1956 he returned to Cuba from exile in Mexico and fought a guerrilla war against Batista that in 1959 succeeded in provoking a change of government.
Castro then set about reforming Cuba along socialist principles, just 150 km off shore of the world's largest foe of communism, the US.
Washington put in place the economic blockade as a reaction for the nationalisation of US property.
In response, Castro formed an alliance with the Soviet Union that was to remain alive for almost three decades.
The fight against the US - portrayed as a David and Goliath struggle in Havana - dominated the life of this Cuban revolutionary.
If he was making a public speech, he rarely missed a chance to attack the northern enemy and accuse Washington of being responsible for economic hardship in Cuba.
At the beginning of this year, the dispute took a bizarre turn. A furious Castro ordered that 138 huge masts with black flags and stars be erected before the US representation in Havana.
They were meant to block from view a sign in one of the upper floors of the building, which broadcast information on human rights.
Each flag symbolised a year in Cuba's long struggle for independence that began in 1868 when Spain was still its colonial master.