Looking for answers, Hélène stumbles across a Norwegian blogger by the name of Mister, who is seriously ill and documents his life with a mix of sincerity and a dry sense of humor.

Even if it is difficult to leave Matthieu behind, Hélène listens to her deepest instinct and travels across Europe all the way to Norway alone in order to be able to find her way.

[10] On 22 February 2018, Screen Daily reported that Emily Atef was preparing her first French-language production entitled Mister.

[9] Producer Xenia Maingot said Atef "wanted to aim high" for the casting of the film and that negotiations were underway with a possible high-profile French actress for the female lead.

[12] Director Emily Atef told French newspaper Le Parisien on 20 May 2022, that it was Vicky Krieps who suggested Gaspard Ulliel for the role of Matthieu because they were friends but had never worked together.

[13] However, in an interview for France's Prèmiere magazine a few days later, Atef said that Krieps suggested Ulliel for the film after meeting him during a casting.

[16][17] Production then moved to Norway on 11 May 2021, followed by a compulsory period of quarantine (due to the COVID-19 pandemic),[13] where it wrapped filming on 4 June 2021.