Cuban President Raul Castro says he will not seek another five-year term after the one he has just started.
On Sunday, he announced that he will step down in 2018 - for the first time putting a date on the end of the Castro era.
He chose rising star Miguel Diaz-Canel as his top lieutenant and first in the line of succession. The 81-year-old also said he hopes to establish two-term limits and age caps for political offices including the presidency - an astonishing prospect for a nation led by him or his older brother Fidel since their 1959 revolution.
The 52-year-old Mr Diaz-Canel is now a heartbeat from the presidency and has risen higher than any other Cuban official who did not directly participate in the heady days of the revolution. "This will be my last term," Raul Castro said, his voice firm.
In his 35-minute speech, he hinted at other changes to the constitution, some so dramatic that they will have to be ratified by the Cuban people in a referendum. But he scotched any idea that the country would soon abandon socialism, saying he had not assumed the presidency in order to destroy Cuba's system.
"I was not chosen to be president to restore capitalism to Cuba," he said. "I was elected to defend, maintain and continue to perfect socialism, not destroy it."
Mr Diaz-Canel replaces the 81-year-old Jose Ramon Machado Ventura, who fought with the Castros in the Sierra Maestra.
Since taking over from Fidel in 2006, Raul Castro has instituted a series of important economic and social changes, expanding private enterprise and relaxing hated travel restrictions. However, the country remains ruled by the Communist Party and any opposition to it lacks legal recognition.
Fidel Castro is 86 and retired, and has appeared increasingly frail in recent months. He made a surprise appearance at yesterday's gathering, receiving a thunderous ovation from politicians.
Some analysts have speculated that the Castros would push a younger member of their family into a top job, but there was no hint of that yesterday.