The actor – best known for his role as Howard Wolowitz in the long-running US sitcom – stars opposite Adam Driver and Marion Cotillard in the musical, which was written by the band Sparks and directed by the French director Leos Carax.
Carax had said he wanted to make sure there were enough Europeans in the film to satisfy quotas that would secure EU funding. Helberg, whose wife is a French citizen and whose children go to a French school, was apparently so keen to be a part of it that he decided to pursue French citizenship.
He told the PA news agency: “I have officially changed nationalities, I became a citizen of France. No big deal, not trying to brag. And I grew a beard, in no particular order.
“But Leos is a genius, he’s a little wizard, and Sparks and Adam and Marion, it’s a group of people that I never imagined would come together that don’t often come together.
“And Leos makes a movie less often than the Olympics, like six or seven years, and I’m just a huge, huge fan of his and Sparks and everybody involved, so I figured this is this is just one of those moments where you have to commit international war crimes, if that’s what it takes.
“And at least it will make a great story at the end of the day if I don’t get the role, so I was pretty bullish about it. I never knew if it was going to pay off, but I loved everything about this thing. And I figured it’s worth it if I die trying.”
Helberg joked he was “a traitor to my country”, but explained he thought the project, which received a standing ovation on the opening night of the Cannes film festival, was worth the effort.
Helberg said Cotillard’s casting actually meant it was ultimately unnecessary for him to become a European for the film to qualify for funding, adding: “I think it was part of the performance art madness that [Carax] was trying to put everybody through it.
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“There always was this question that I had, which was is he just like a wicked man who’s asking us to do all of these insane things because it’s part of the process or because that kind of chaos makes people more vulnerable or more creative?
“I don’t think it was so with the EU subsidy part of the film, but I do think throughout there was a quality actually that he perpetuates, which is this tenuous sort of precariousness of ‘Will we fail? Is this even possible?’
“And then when you’re asked to really go for something that seems just absolutely untenable, something very creative comes out of that and I think maybe that that’s kind of where he idles.”
Helberg also joked that his role as The Accompanist is the “underbelly” of the pianist character he played in the film Florence Foster Jenkins, opposite Meryl Streep and Hugh Grant, about the eccentric opera singer.
Annette is out now in UK cinemas.
Additional reporting by PA
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