Alexander De Croo resigned after his Flemish Open party, the Liberals and Democrats, fell in the Belgian elections.
Belgium has begun its search for a new governing coalition after elections pushed centre-right parties into prime positions across the country in a rare alignment.
In Sunday's regional and national vote, the conservative New Flemish Alliance (N-VA) maintained its decade of control in Dutch-speaking Flanders, edging out the far-right Vlaams Belang in second place.
Meanwhile, in French-speaking Wallonia, the center-right Reform Movement shattered the long-standing supremacy of the Socialist Party. They also took first place in Brussels.
On Monday, Prime Minister Alexander De Croo, who had seen support hemorrhage in his Flemish Liberals and Democrats party, handed in his resignation to King Philip as per protocol.
“This is an extremely tough night for us. We have lost this election,” De Croo said, adding that he would take full responsibility for the loss.
N-VA chief Bart De Wever, current mayor of Antwerp, could be the prime ministerial candidate most likely to get the initial nod, as his party won the most seats (24) in the federal parliament of 150 seats.
“We are completely moving away from the traditional Belgian narrative of the last 50 years, according to which Flanders is on the right and Wallonia on the left,” Vincent Laborderie, a professor at UCL University in Leuven, told AFP.
“We have the impression of a structural shift of the electorate towards the center-right.”
In the coming months, Belgium's political parties will seek to forge a governing coalition between the largely center-right parties of the Dutch-speaking north and the more left-wing parties of the French-speaking south.
With its complex regional and national system, Belgium has an unenviable record of painfully protracted coalition discussions, reaching 541 days in 2010-2011.
“Logically, this time we should go faster,” Laborderie said, suggesting it would take six months to find a “landing.”
Meanwhile, De Croo will remain interim prime minister.
