Backstage at Jason Wu at New York Fashion Week

When the masses arrived at the Jason Wu show on Friday, it was official: the first big show of fashion week was here. It felt a little bit like a back-to-school party for the fashion world after summer camp, hugs and "you look incredibles," all around.

Backstage, things were similarly serene. Carolyn Murphy—the classic supermodel who Wu had lined up as his big "surprise" guest—prevailed over the room like a patron saint. As I raised my camera to snap a picture of her getting into her hair and make-up (yes, I am that girl), a chipper publicist raced towards me. "If you take photos of Carolyn, please don't upload them until after the show, OK?" Fine. What is a surprise anymore, really? With tweeting and Instagramming from backstage going at this rate, it's impossible to protect the big reveal anymore.

But when Wu's clothes hit the runway, it still felt like a shock. It was the sexiest collection he had produced in a long time. The designer said that he was inspired by the photographers Helmut Newton and Lillian Bassman—a provocative point of view and a feminine one, wrapped into the same collection. "What I found in common between the two of them was an appreciation of the feminine form," he told me after the show. "And identifying the female body." There were high-waisted leather shorts, dresses with harnesses, and then dream-like tulle ball gowns.

It was almost four years ago that Michelle Obama took the stage at the Inaugural Ball in a one-shouldered white dress designed by Wu. It effectively put him on the map. And in four years, a lot about the Obamas has changed. But Wu has evolved too.

"Ever since then, I didn't want to take it all in stride," he says. "I wanted to mature as a better designer every season. And I think this collection more than ever, you'll see the grown-up version of Jason Wu."