WARSAW, Poland (AP) — Former European Council president Donald Tusk said Monday he is backing the main opposition candidate in Poland's May presidential election.

Tusk was Poland's prime minister from 2007-2014 and remains associated with his centrist pro-European Civic Platform party that is now the main opposition force in Poland, but enjoys steady support, chiefly in large cities.

He said he supported “with all my might and my whole heart” the party's candidate, Deputy Parliament Speaker Malgorzata Kidawa-Blonska, saying she would bring peace into Poland's stormy politics under the ruling right-wing, populist party.

The incumbent, Andrzej Duda, who is aligned with the ruling Law and Justice party, is seeking re-election for a second five-year term.

Recent opinion polls show he might face a serious challenge from Kidawa-Blonska and from the leader of the pro-European Polish People's Party, Wladyslaw Kosiniak-Kamysz.

Tusk is now head of the European People's Party, of which the Civic Platform is a member.