Otelo Saraiva de Carvalho, the military officer who planned the coup that became the Carnation Revolution, needed a signal every unit could receive on an ordinary radio, at an exact moment, without anyone outside the plot understanding what they were hearing. His first choice was another José Afonso song, "Venham Mais Cinco," but the radio host helping plan the broadcast, João Paulo Diniz, talked him out of it: the song was one of the many Afonso compositions Estado Novo censors had banned as suspected Communist propaganda, and airing a banned song, on any station, at midnight, would have drawn exactly the attention the plot needed to avoid. "Grândola, Vila Morena," a 1964 tribute Afonso wrote to a working-class musical society in the Alentejo town of Grândola, had somehow escaped the censors entirely, an ordinary folk song by an artist the state watched closely.
The plan used two signals rather than one. At 22:55 on April 24, Paulo de Carvalho's Eurovision entry "E Depois do Adeus" aired on a different station, alerting officers to prepare. Then, at 00:20 on April 25, Radio Renascença played "Grândola, Vila Morena," the operational go-ahead. Within hours, Armed Forces Movement units loyal to the plot occupied Lisbon's military headquarters, airports and government buildings, and by the next day Portugal's authoritarian government had fallen, leaving a Catholic radio station's late-night broadcast of an unbanned folk song as the exact moment historians point to when the Carnation Revolution began.