When the French director Catherine Breillat was 40, her then-husband and the father of her first child ended their relationship to be with a much younger woman. Soon after, Breillat started dating a man 12 years her junior.

“Men want to repudiate their wives of a certain age by saying they couldn’t be loved by anyone anymore,” Breillat said in a recent video interview via an interpreter. “But for me that’s not true. I want to tell other women there’s no cause for despair.” In “Last Summer,” which comes to theaters Friday, she probes at this realization through an incendiary premise.

Since the 1970s, the lauded director, now 75, has repeatedly focused her unflinching gaze on the troubled sexual awakenings of girls, often in the uncaring hands of older men, but in “Last Summer,” that dynamic is inverted: A middled-aged lawyer, Anne (Léa Drucker), risks her career and marriage by having a clandestine affair with her 17-year-old stepson, Théo (Samuel Kircher).

The film, Breillat’s first in a decade, joins several recent movies concerned with the power dynamics of heterosexual couples in which the woman is older, including the lighter Anne Hathaway-vehicle “The Idea of You” and Todd Haynes’s divisive “May December.” (Haynes’s movie was inspired by the true story of a teacher who started a relationship with one of her students.)

According to Breillat, this wave of films reflects a simple reality. “It’s the truth,” she said: “Young people are attracted to older women.”

While “May December” positions the young man as a victim grappling with conflicted feelings, Breillat instead made the teen in her movie “not only the object of desire, but the subject of desire,” she said, and the one who “presses for this affair to take place.” Breillat refuses to pass judgment on either of her characters, and instead chronicles how the illicit desire consumes them both.

“I find such a portrait far more interesting than the moralizing society loves to engage in,” she said.

Part of Breillat’s motivation in making “Last Summer” — which is a reimagining of another film, the 2019 Danish drama “Queen of Hearts” — was to interrogate the idea of the “cougar” (a term she hates) and the social norms that suggest “if it’s a woman who is seen with a younger man, you assume he is only with her for financial reasons,” she said.

In her nearly five-decade career, which includes acting in the scandalous Bernardo Bertolucci film “Last Tango in Paris,” female sexuality has been the primary concern of Breillat’s work.

“Few directors get as deeply under the skin as Breillat, a longtime, reliably interesting provocateur who tests the limits of what the world thinks women should do and say and be,” wrote Manohla Dargis in her Times review of “Last Summer.”

Breillat’s fearless exploration of desire onscreen, however, has sometimes elicited pushback in France, where she has rarely been recognized. If it weren’t for the positive reception to her work in English-speaking countries, Breillat said she believes her career in her home country would be nonexistent.

When she released the 1988 feature “36 Fillette,” in which a playboy in his 40s manipulates a 14-year-old girl into a sexual relationship, French critics, Breillat recalled, claimed it was “the worst French film ever made.”

“I was criticized for having a male protagonist who was a ‘caricature,’” she said. “And of course, the #MeToo movement has shown that I never invent anything in my cinema, that what I portray is a reality.”

Although she is known for the sometimes-explicit moments of intimacy in her work, Breillat said she didn’t think of “Last Summer” as a story in which carnal pleasure was the focal point. “This film is about the dark side of desire,” she said.

Still, “Last Summer” features three sex scenes between Anne and Théo, each one at a distinct point in their doomed liaison. Their nakedness, however, remains deliberately offscreen. “You don’t have to shoot their bodies,” Breillat said. “The transcendent emotions they are undergoing are only visible on their faces.”

In focusing on their agitated visages, Breillat said she was interested in wondering what the characters were thinking while engaging in the sexual act. What are they imagining?

“Love is about telling yourself stories; it’s about projecting yourself onto a relationship,” she said. “Therefore, it’s a fiction. It’s about thought. It’s about ideas.”

Breillat said she is vehemently against employing intimacy coordinators, whose job, she said, was more about “putting blinders on the eyes of the viewers,” than ensuring the actors’ emotional safety. In her view, that’s what the director is there for. “If a director isn’t capable of staging such a scene, then they simply shouldn’t do them,” she said.

There’s always fear involved in filming sex scenes, Breillat said, because they require utter vulnerability. For the French provocatrice, that’s how it should be.

“What’s the point of making films if you’re not going to be afraid, if the stakes aren’t so crucial that they’re about what’s at the heart of our existence?” she said.