WARSAW, Poland (AP) — A Russian prankster posing as the U.N. secretary-general managed to reach Poland’s president on the telephone and rendered him speechless with questions about Ukraine, Russia and his reelection on Sunday.

The prankster, Vladimir Kuznetsov, known as Vovan, posted a recording of the 11-minute call on YouTube. President Andrzej Duda's office confirmed Wednesday that it was authentic.

At various points in the conversation, conducted in English, Duda sounds surprised at the line of questioning but still refers to the impostor as “Your Excellency.”

Duda tweeted Wednesday that he realized “something was not right” during the conversation, which took place Monday afternoon while the president awaited official word of his election victory.

Duda said he was suspicious because the real United Nations chief, Antonio Guterres does not pronounce the name of Polish vodka brand Zubrowka as well as the caller did. But he conceded that the “voice was very similar.” The president ended his tweet an emoticon of tears of laughter.

Polish state security is investigating how the prankster got through to the president and whether Russia's secret services were involved.

The Internal Security Agency said in a statement the call had been authorized by an official with Poland's mission to the United Nations and that his actions are under investigation.

Poland's relations with Russia are tense, especially over Poland's support for Ukraine's drive for closer links with the European Union.

The caller congratulated Duda on his reelection but took the president to task for his hostile campaign comments about the LGBT community, drawing Duda's assurance that he has “huge respect for every human being.”

Duda also rejected a provocative suggestion that Poland would seek to claim back the Ukrainian city of Lviv, which was part of Poland before World War II.

“No! No! This is Ukraine,” Duda emphasized, adding that no political group in Poland harbored such an idea.

The president also said that Poland has a “discussion about history” with Russian President Vladimir Putin about World War II and the Soviet “occupation” of Poland after the war.

Kuznetsov, and the Russian prankster Alexei Stolyarov, who is known as Lexus, have previously embarrassed European politicians including French President Emmanuel Macron and British Prime Minister Boris Johnson, as well as Elton John and Prince Harry with similar hoax calls.