“In the space of four years, Lilou emerged from secrecy. She became a 64-year-old woman who enjoys DIY projects, gardening, cycling, and spending time with her grandchildren,” reads the synopsis for a new film called A Secret Heart (Cœur Secret). “By documenting her transformation, I filmed a family healing its wounds and reinventing a place for each member. This family is my family; Lilou is my father.”

A Secret Heart world premieres on Thursday, May 14, in ACID, the Cannes Film Festival sidebar run by France’s association of film directors.

The documentary is the feature directorial debut of 33-year-old French director Tom Fontenille, who also handled the cinematography and wrote the film with Valentine Bonnaz. The editor is Marie Bottois. A Secret Heart was produced by 5A7 Films, with Gabin and Fiume o morte! seller Lightdox handling international sales.

“In this family chronicle, each member is forced to readjust their place and confront what had remained buried and hidden,” reads a summary on the ACID website. “Little by little, a discreet but irreversible metamorphosis takes hold.”

Or as ACID general delegate Pauline Ginot puts it: “We start with a family of four whose lives are set in motion along several storylines: mourning the mother, the father undergoes a revolution, begins a gender transition, and then drags everyone along with him. An intimate family documentary – one that couldn’t be more humble – that also turns out to be a melodrama and a family epic.”

Ahead of the film’s premiere, Fontenille shared with THR details of his family’s cinematic and personal journey that resulted in A Secret Heart.

“In the beginning, the idea was not to make a film,” he recalled. “When I started to film my father, it was because I wanted to [address] difficult things in my family – my mother’s death, for example. And it was really difficult to communicate with my father. So, I started to just film our conversations, and in the beginning, my father was really reluctant.”

Then, one day, he asked his son to show him some of the footage and shared that he liked it. “Your images are beautiful,” the director recalls the surprising reaction. Just before that, Fontenille and his sister had found women’s clothes in their father’s cupboard. “We realized that he was cross-dressing,” the director told THR. “When my father saw my [footage], he told me: ‘You can film me when I’m wearing women’s clothing,’ too.”

That’s when the filmmaker made a decision. “I started to believe there was a film, because of my father’s interest, and because of this new space that was opening to her and to me,” Fontenille explained. “And I believed at that time that this was a theme for everyone, because there are universal themes, universal subjects” addressed in the film.

Fontenille also felt the filming process provided a space and time of “introspection” for his father and himself. “You have to understand and to touch on vulnerability to build the future from that,” he shared. “I think we knew that, not really consciously, but we felt it. And I knew it was the path I had to take to make me better and make my family better as well.”

He worked on A Secret Heart for five years and finished the film after the death of his father. Lilou may not have seen the final version, but got regular sneak peeks at it. “I used to show her a lot of images and a selection [of footage],” said Fontenille. “It looked good to her. But sometimes she just said, ‘Oh, there is too much dialogue.'”

Premiering at ACID in Cannes is a dream come true for the filmmaker. “We couldn’t hope for anything better,” he told THR. “And I think it’s good for my father as well. I know it was very important for her to show this film, and we had a lot of discussions about this. She believed this kind of movie could be a great way to make people aware of the subject and also help the family. That’s why it was really important for her, for me, for my sister, and, I could say, for my mother as well. So, I’m really happy, and I think my father is going to live [on for] a long time now,” Fontenille concluded while pointing to the heavens. “And I know she’s happy somewhere.”