The man expected to become Belgium's next prime minister has caused a stir by singing the French national anthem when asked to sing the Belgian one.
Yves Leterme is struggling to form a coalition
Yves Leterme, head of the Flemish Christian Democrats, broke into La Marseillaise instead of Belgium's La Brabanconne on the national day.
His gaffe was filmed by Belgian RTBF television, as he was about to attend a church service in Brussels on Saturday.
Dutch- and French-speaking politicians are struggling to form a new coalition.
The outgoing coalition led by Prime Minister Guy Verhofstadt is still governing in a caretaker role as negotiations continue.
Clips of Mr Leterme's gaffe have been broadcast on the internet video site YouTube.com.
Footage of him at the church service also showed him failing to sing along to La Brabanconne.
Vague on history
He also made a mistake over Belgium's national day, saying it marked the "proclamation of the constitution". It actually commemorates the inauguration of Leopold I as the country's first king on 21 July 1831.
According to an opinion poll cited by RTBF, just one in five Belgians knows why Belgium has its national day on 21 July.
Mr Leterme's party made big gains in last month's election, ending their eight years in opposition. They won 30 seats in the 150-seat lower house.
Mr Leterme says he wants to increase the autonomy already enjoyed by Flanders, the Dutch-speaking northern region where 60% of Belgians live, and French-speaking Wallonia in the south.
No single party bridges the linguistic and geographic gulf between Belgium's two regions.
Traditionally, the prime minister comes from one of the majority Flemish parties.