Nationalist historian Karol Nawrocki won Poland’s presidential election, official results showed on Monday, in a major blow for the country’s pro-European Union (EU) government.

The 42-year-old, an admirer of US President Donald Trump, scored 50.89 percent of votes in Sunday’s runoff, the national election commission said.

His 53-year-old rival Rafal Trzaskowski, Warsaw’s pro-EU mayor and an ally of the country’s centrist government, won 49.11 percent in the highly polarized North Atlantic Treaty Organization and EU nation.

“Congratulations to the winner!” outgoing conservative President Andrzej Duda said on X.

Duda, who had endorsed Nawrocki, thanked Poles for “carrying out your civic duty” and for the turnout, which was 71.63 percent.

The results followed a tense evening as both candidates had claimed victory when an exit poll indicated they were neck and neck.

“We will win and we will save Poland,” Nawrocki told a crowd of supporters at his election night rally in Warsaw soon after polling stations closed.

Nawrocki’s win will block the government’s progressive agenda for abortion and LGBTQ rights and could revive tensions with Brussels over rule of law issues.