Those sneaky French - turning a romantic comedy into a trilogy, maybe even a franchise, without even telling us.

It started in 2002, in Barcelona, with a bunch of foreign exchange students - meeting, flirting and falling into one another’s arms in “L’Auberge Espagnole” (“The Spanish Inn”).

It continued in London, Paris and St. Petersburg with “Russian Dolls” (2005).

And now, as the characters and the actors playing them - Romain Duris, Audrey Tautou, Kelly Reilly, Cecile de France - push 40, they collide once more. This time they’re in New York, in Manhattan’s Chinatown, in “Chinese Puzzle.”

“I love the idea of following these characters in their 20s, 30s and 40s,” says writer-director Cedric Klapish, who is 52. “You don’t cover the same subjects you would in an ordinary movie. You’re talking about time passing, getting older, how a person changes from his 20s to age 40. The dreams you have when you’re 25 that change when you’re older - what you want to become vs. what you actually became.”

Klapisch doesn’t call the films a trilogy, and never really warned the actors that he’d be coming back to them and taking the story further. But they all signed on. Duris, who turned 40 this week, was lured back by the parallels he saw between the script and real life.

“This business of not growing up until you’re 40, that must be universal, yes? Your decisions and choices have consequences that they did not have at 25,” Duris says. He plays Xavier, the writer who has split from his Irish wife (Reilly) but who follows her to New York to be near their children. “At 25, you’re full of youth and pursuing a career, a lover, but maybe not for life. We see Xavier making decisions in ‘L’Auberge Espagnole’ that seem, to him, to be very very important. But we, the audience, know how tiny his problems are, how insignificant his decisions are.”

Xavier struggles to settle into New York, find an apartment, to master the moods of the Immigration and Naturalization Service, to raise his kids and meet the needs of his needy lesbian friend Isabel (De France) and her partner.

With each location, the characters - mostly French - cope with a new city and a new pace of life. From laid-back Barcelona, to go-go London, the long-lunches, longer-vacations of Paris, to patience-testing St. Petersburg, the scene shifts to the City that Never Sleeps - New York.

“They are two cities that dream of each other,” Klapisch says. “Paris dreams of New York, New York dreams of being more like Paris.”

“The electricity of the streets, that magic energy the city has like no other,” Duris adds. “When you go out, there’s just something in the air. It was great to play with that in the movie, the rhythm of the streets, and of the people, working in Chinatown, wherever. The pace of life is fast in Paris, and has gotten faster since I was a child. It is the most electric city in France. But New York? It’s on another level. The whole world is here, young and old, all these different cultures. And they’re all moving.”

Not that either Frenchman doesn’t prefer Paris, which can be “stimulating, and yet, peaceful where you don’t hear noise all day and all night,” Klapisch says. “You can have a long lunch, and long vacations. I love that about the French life. You can enjoy food more, leisure time more. Maybe the best would be a mix of the two, half New York, half Paris.”

“Maybe something like Hong Kong,” Duris offers.

Wait, that sounds like another movie. Will we be seeing this quartet again, at 50?