Eisenberg wrote, directed and starred in the film, about two American cousins who travel to Poland to honour their grandmother, a Holocaust survivor, who was based on Eisenberg’s own great aunt.

He told the citizenship ceremony: “While we were filming this movie in Poland, and I was walking the streets and starting to get a little more comfortable in the country, something so obvious occurred to me, which is that my family had lived in this place for far longer than we lived in New York.

“And of course, the history ended so tragically.”

He continued: “In addition to that tragedy of history is also the tragedy that my family didn’t feel any connection any more to Poland, and that saddened me and confirmed for me that I really wanted to try to reconnect as much as possible.

“And I really hope that tonight in this ceremony and this amazing honour is the first step of me, and on behalf of my family, reconnecting to this beautiful country.”

Eisenberg was inspired to make A Real Pain after the death of his great aunt Doris at the age of 106 in 2019. She grew up in Poland but fled to the US in 1938. Other family members who remained in Poland were killed during the Holocaust.

President Duda said: “I am delighted that people from across the ocean acknowledge their heritage, recognise that their ancestors hail from the Republic [of Poland] and seek to forge a connection with our country.”

Eisenberg was nominated for an Oscar for writing the film, while his co-star Kieran Culkin won the award for best supporting actor.

“It’s like this guy is… doing things that are problematic, taking away fact-checking,” Eisenberg told BBC Radio 4’s Today programme. “[There are] safety concerns. Making people who are already threatened in the world more threatened.”

Meta announced last month it would no longer use independent fact-checkers on Facebook and Instagram, replacing them with X-style “community notes”, where commenting on the accuracy of posts is left to users.

In a video posted alongside a blog post, Mr Zuckerberg said third-party moderators were “too politically biased” and it was “time to get back to our roots around free expression”.

But Eisenberg told BBC News he was “concerned”.

“These people have billions upon billions of dollars, like more money than any human person has ever amassed and what are they doing with it?” he said.

“Oh, they’re doing it to curry favour with somebody who’s preaching hate.

“That’s what I think… not as like a person who played in a movie. I think of it as somebody who is married to a woman who teaches disability justice in New York and lives for her students are going to get a little harder this year.”

Legal settlement

Meta’s move came as Mr Zuckerberg and other technology executives sought to improve relations with US President Donald Trump, ahead of his inauguration.

Trump and his Republican allies had criticised Meta’s fact-checking policy, as censorship of right-wing voices.

And after the changes were announced, Trump told a news conference he was impressed by Mr Zuckerberg’s decision and Meta had “come a long way”.

Last week, Trump signed a legal settlement that will see Meta pay out roughly $25m (£20m).

He had sued the company and Mr Zuckerberg, in 2021, over the suspension of his accounts after the 6 January Capitol riots.

Oscar nomination

Eisenberg is promoting A Real Pain, which he wrote, directed and stars in – a comedy drama about two cousins who travel to Poland together to visit Holocaust sites to honour their late grandmother.

The grandmother is based on Eisenberg’s real-life Aunt Doris and was filmed at the home his family used to live in, in Poland.

In the movie, the cousins struggle to reconcile their own modern life problems against the backdrop of one of the 20th Century’s most devastating and horrific events.

Eisenberg’s screenplay has received an Oscar nomination, as has his co-star, Kieran Culkin.

“Grandchildren of Holocaust survivors should wake up every morning and go outside and kiss the ground that they’re alive and thank whatever god they pray to – as the world didn’t want them to be alive,” Eisenberg told Today.

He said he had “tried to connect to bigger things” since making the film.

“I live in a world that feels hedonistic, my life is maybe too easy.”

He added that it was essential the film had a comic feel.

“It would be so sanctimonious without any humour in it.”

Eisenberg was also nominated for an Oscar for his portrayal of Mr Zuckerberg in The Social Network.