It was when the head of the United Nations suggested a land grab of neighbouring Ukraine that Poland’s newly re-elected president must have realised that something was not right. The posting of the 11-minute phone call on YouTube confirmed it. The caller, whose topics of discussion ranged from coronavirus to US President Donald Trump, was not Portuguese UN Secretary-General Antonio Guterres, but a Russian prankster following a well-trodden path of duping world leaders. The latest target was Andrzej Duda, who narrowly won re-election as president at the weekend, but whose calm was shaken by his apparently distinguished caller’s line of questioning. Mr Duda’s office confirmed the call was genuine. Poland’s state security is now investigating how Vladimir Kuznetsov, known as Vovan, managed to get through to the president and whether Russia’s secret services were involved. The country’s security agency said the call had been authorised by a Polish mission official at the UN, 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. Speaking in heavily accented English, Vovan congratulated Mr Duda on his re-election before asking him if he wanted to claim back the Ukrainain city of Lviv, that was part of Poland before the Second World War. “No, this is Ukraine!” spluttered the president. “No, no, no, Excellency, there is no discussion about it in Poland. No. Now this is part of Ukraine and this is the end. No, no, no.” He added: “We are in very good relations with Ukraine, we support them.” The conversation ranged over Polish political personalities, relations with Russia and whether Mr Duda had been personally congratulated by Mr Trump. Vovan, and the Russian prankster Alexei Stolyarov, who is known as Lexus, have 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.