Socialist leader Mr Jose Luis Rodriguez Zapatero was sworn in as Spanish prime minister today by King Juan Carlos, completing a shakeup of Spanish politics in the wake of last month's train bombings.
The solemn ceremony at the Zarzuela palace near Madrid was also attended by Queen Sofia and outgoing Prime Minister Jose Maria Aznar.
It was the last formal step to Mr Zapatero taking office after he was approved by parliament yesterday, nearly five weeks after the Socialists' upset win in general elections. The poll was held three days after the March 11th attacks that killed 191 people.
"I promise on my conscience and honour to comply faithfully with the obligations of prime minister, to be loyal to the king and preserve the constitution as the basic rule of the state," Mr Zapatero said.
He chose to take a non-religious oath of office - promising with his hand on the Spanish constitution - rather than to swear on the Bible.
Mr Zapatero (43), becomes Spain's fifth prime minister since democracy was restored following the death of dictator Francisco Franco in 1975.
Later today, Mr Zapatero was expected to move into the elegant Moncloa building, the prime minister's official residence on the outskirts of Madrid.
He was also due to have a private meeting with King Juan Carlos to inform him of the members of his cabinet, who will be sworn in tomorrow.
Mr Zapatero has caused controversy with his pledge to withdraw Spanish troops from Iraq if the United Nations does not take charge there by June 30th.