Donald Tusk, the head of the European Council, was grilled in his native Poland for a parliamentary investigation into a pyramid scheme that cheated thousands of Poles out of their savings during his time as prime minister.
In an emotional moment, Mr Tusk called his televised questioning a “spectacle” aimed at discrediting him and spreading “insinuations” about his family.
There have been years of enmity between Tusk and Poland’s ruling Law and Justice party leader, Jaroslaw Kaczynski.
Commentators on private TVN24 described the event as a public “grilling”, and it was widely seen as part of the conservative party’s efforts to discredit Mr Tusk, a political foe who is still popular in Poland.
Mr Tusk was sworn in by the special multi-party commission that has already questioned dozens of state officials in its efforts to pinpoint responsibility for the scam.
Addressing him as “prime minister” the commission sought to determine the scope of Mr Tusk’s authority over state security and other offices and when he was made aware of the pyramid scheme by the Amber Gold financial institution.
Prosecutors say some 19,000 investors lost over 850 million zlotys (£173 million) in what turned out to be one of the biggest financial scandals in Poland.
Amber Gold’s founders are now serving prison terms.
The scam, which was revealed in 2012, has raised questions about the effectiveness of Poland’s government during Mr Tusk’s 2007-2014 term.
Authorities allegedly failed to react in time to warning signals about Amber Gold, which turned out to be a pyramid scheme.
Rejecting these allegations, Mr Tusk said a warning against Amber Gold was issued by a Polish financial supervision body and it was not the prime minister’s job to make such a warning.
One of the themes of the investigation and of Monday’s questioning was the fact that Mr Tusk’s son Michal was employed by an airline owned by Amber Gold.
Mr Tusk denied allegations that his son’s job could have served as a protective umbrella for the pyramid scheme.
He said it was then that the investigation started, but stressed he would not link these two facts together.
There was no escaping the political overtones of Monday’s interrogation.
The commission’s head, Malgorzata Wassermann of the Law and Justice party, on Sunday lost her bid to become mayor of the city of Krakow.
Those local elections across Poland made the ruling party aware that its appeal to city voters is limited.
For his part, Mr Kaczynski claims that negligence under Mr Tusk was the reason for the 2010 plane crash in which his twin brother, President Lech Kaczynski, was killed.
Mr Tusk and the president had a rocky relationship.
The investigation into the plane crash in Smolensk, Russia, which killed 96 state, military and other officials, said it was due to human error in poor visibility at a rudimentary airport.