Cuban President Raul Castro's son, Alejandro, was the communist island's envoy for secret negotiations with the United States that led to the countries' historic rapprochement, a cardinal close to the talks said.
Speculation had long swirled that Alejandro Castro Espin, the president's 51-year-old son, headed up the secret talks.
But the confirmation from Cardinal Jaime Ortega, the former archbishop of Havana, is the most official namedrop to date -- and further boosts the profile of Castro Espin, who is touted as a possible future president of Cuba.
Castro Espin was "at the head of the Cuban delegation," Ortega said in a speech to a conference in the United States that was published in the latest issue of Cuban Catholic magazine Secular Space (Espacio Laical).
Ortega, who recently stepped down as head of the Cuban Church, represented the Vatican at the talks, which Pope Francis played a key part in brokering.
The US delegation was led by Ricardo Zuniga, a top adviser to then US president Barack Obama.
The negotiations led to the announcement of a rapprochement in December 2014 after more than half a century of Cold War hostility.
Castro Espin, an army colonel, is an international relations expert.
The president's only son, he kept a low profile for years. But he was present when his father and Obama held their first-ever talks in Panama in April 2015.
Many observers now tip him to be a major player in the power transition due next February, when Castro is due to step down.
Vice President Miguel Diaz-Canel, 56, is seen as Castro's heir apparent. But Castro Espin is increasingly viewed as a president-in-waiting.
Ortega also unveiled another mystery of the US-Cuba talks, saying the date of the rapprochement announcement -- December 17 -- was chosen because it is Pope Francis's birthday.