Five months after a general election, the opposition candidate Irfaan Ali has been sworn in as Guyana's president.
Following allegations of vote tampering, a recount and a lengthy legal battle, the election commission declared Mr Ali the winner on Sunday and he was sworn in hours later.
His rival, outgoing president David Granger, said he would take his allegations of fraud to the high court.
Oil giant Exxon Mobil recently began producing oil off Guyana's coast.
The discovery of huge oil reserves in Guyanese waters over the past years meant that the election was much more closely watched than previous ones as the new president will be the one to administer the windfall resulting from the find.
What happened in the election?
The election on 2 March pitted the 75-year-old incumbent David Granger, of the People's National Congress, against 40-year-old Irfaan Ali of the People's Progressive Party.
Mr Granger declared victory days after the vote but international electoral observers said counting in Guyana's most populous electoral district, Region Four, had been "interrupted" and was "incomplete".
The opposition alleged that the result in Region Four had been inflated in Mr Granger's favour.
Guyana's Supreme Court initially ordered a partial recount but after weeks of wrangling, a full recount was held.
Preliminary data suggested the opposition had won the election but the Guyana Elections Commission (GECOM) did not declare Mr Ali as the winner until Sunday.
GECOM also announced that Mr Ali's coalition had won a narrow majority 33 of the 65 seats in parliament with Mr Granger's A Partnership for National Unity coalition winning 31 seats and another coalition claiming the remaining seat.
Why does it matter?
The election was the first to be held after the US oil giant Exxon made one of the world's biggest discoveries of oil in deep waters off Guyana's coast.
The discovery could put Guyana among the world's top oil producers and is expected to massively boost its economy.
One of the main topics of the presidential campaign was how to use the windfall from the discovery.
Mr Ali and his party have been critical of the contract the outgoing government signed with Exxon saying it was not favourable enough to Guyana.
Mr Granger said that while he respected "the lawful consequences" of the announcement by the elections commission declaring Mr Ali the winner, he would take the allegations of electoral fraud to the country's supreme court. He also appealed to his supporters to remain peaceful.
Mr Ali called for unity saying that "there is only one future and that future requires a united Guyana, that future requires a strong Guyana".
He also said that he would be naming his cabinet soon and promised "a government that is accessible and one that will be more than willing to share with you information as we work on building our Guyana in the interest of all".