When director Matt Tyrnauer set out in 2005 to make the documentary Valentino: The Last Emperor, he had no idea that his film would capture the designer’s final bow.

During the filming, Tyrnauer and his team had unprecedented access to both Valentino and Giancarlo Giammetti, Valentino’s lifelong business partner and long-ago boyfriend. But on the subject of the designer’s retirement—which was announced not long after his extravagant 45th anniversary celebration in the summer of 2007—both men played their cards very close to the vest.

“Even in the course of the movie you see journalists asking if he’s going to retire and he won’t say. As much time as I spent around Valentino and Giancarlo, they really wouldn’t tell me, either,” Tyrnauer, a special correspondent for Vanity Fair, says. “They also changed their minds all the time, so that’s part of their character. It really was a mystery. I think none of the press in Italy knew. I don’t even think their closest associates knew.”

One of the most engaging aspects of the film, which was shot in seven locations, including at Valentino’s homes in Rome, Gstaad, and Manhattan, and on his 152-foot yacht, The T.M. Blue One, concerns Valentino and Giammetti’s 50-plus-year relationship—jokes, insults, tears, and everything in between. “Valentino is allowed to exist in this rarefied world that doesn’t have real difficulties in it because Giancarlo protects him from everyone,” says Tyrnauer. “But that’s part of the relationship that I found so extraordinary. For them, they were extremely open for the first time, and I’m not sure what the motivation for that was other than that it was time.”

As for the duo’s reaction to the film, Tyrnauer says they were “a bit traumatized” initially, but standing ovations after the premieres at the Venice and Toronto film festivals provided reassurance. “Sometimes near the end of your career you feel like you need a witness to what it was,” Tyrnauer says. “I think that Valentino wanted to be witnessed on film. He had fulfilled his dream of being one of the greatest fashion designers ever, but I think he had another secret dream, which was to be a movie star… so this is another form of that.” Valentino: The Last Emperor opens March 18 at the Film Forum, 209 West Houston, 212-727-8110.