Gyllenhaal plays a real-life newspaper cartoonist in Zodiac
As Jake Gyllenhaal sits giving interviews about his new film Zodiac, in competition in Cannes, a speedboat full of paparazzi bobs up and down in the Mediterranean behind him.
"Don't know what they're looking for," says the relaxed actor - but he is aware this is his life now.
Donnie Darko may have made him a cult hero, but Brokeback Mountain - the
2005 movie known forever in critic shorthand as "the gay Western" - made him an Oscar-nominated superstar.
Gyllenhaal's first festival experience was seeing Brokeback Mountain win Venice's Golden Lion, after Cannes had rejected it for competition.
"When we came to Venice with Brokeback Mountain, we were sort of blown away by the response.
"This is bigger, and more glamorous, and yet really focused on the film-maker," he says about his first Cannes visit.
Brokeback Mountain won Gyllenhaal his first Oscar nomination
He adds: "Venice is beautiful, but I never got to do my interviews by the ocean. This is great - it's beautiful."
Zodiac, directed by Fight Club's David Fincher, is a thriller about the "Zodiac" serial killer who terrorised California in the 1970s, taunting the authorities with cryptic messages. He was never caught.
The film, also starring Robert Downey Jr, Mark Ruffalo and Chloe Sevigny, opens in the UK on Friday after positive reviews, but modest box-office returns in the US.
Gyllenhaal plays the real-life Robert Graysmith, a newspaper cartoonist who was among a number of men who became obsessed with solving the crimes.
Gyllenhaal stars opposite Robert Downey Jr in Zodiac
"I was nervous about meeting Robert Graysmith, because I thought, 'What kind of person destroys their life and gets involved in something like this? They must be pretty sinister and dark,'" he says.
"Then I met [Graysmith] and he's this really nice guy, who's sort of an innocent.
"He just enjoyed puzzles. He just needed to find that last clue to the crossword puzzle."
Fincher has previously tackled the subject of a serial killer in the inventive and acclaimed 1995 film Seven.
The new film is also "not your typical serial killer movie", says Gyllenhaal.
"It's about the obsession behind that, and the type of person that it takes to do that.
"And I don't think any serial killer movie has got into that idea like this movie has."