Alexa Chung, Maggie Gyllenhaal and Ashley Olsen at the YSL Belle D'Opium Launch Party Photo: Getty Images

When you're a famed French fashion house launching a new version of an iconic fragrance, the celebs come out to play.

Such was the scene last night when Yves Saint Laurent debuted the much-anticipated Belle D'Opium to the New York crowd, and Maggie Gyllenhaal, Ashley Olsen, M.I.A., Tinsley Mortimer, Katie Lee Joel, Shosanna Lonstein Gruss and Alexa Chung all dropped by for a whiff.

French actress and Belle D'Opium face Melanie Thierry. Photo: Getty Images

"I'm up past my bedtime," Katie Lee Joel told StyleList, when the willowy brunette took a turn on the red carpet close to 10pm.

And asked what fragrance she had chosen for the special night, the ex-wife of Billy Joel had a surprising answer.

"Nothing - I really don't wear perfume. But maybe that'll change after tonight!"

Elsewhere on the red carpet, Mortimer spoke of hopes to start her own brand ('I don't know what exactly I'd sell yet, but it would have my name on it,' she said), and Gyllenhaal wowed in a peony pink Yves Saint Laurent Edition Soir 2010 strapless silk dress and Hamptons black rope sling back sandals, while Chang drew second takes with her high-waisted leather shorts featuring mid-thigh cut-outs.

Party guests were led into the 'experience' - a trippy 3D surround-sound theater with an IMAX-like screen that wrapped around the circular room for a panoramic view. As sultry French actress Melanie Thierry -- who was also at the party wearing a sexy YSL black lace dress and black satin pumps -- writhed around the screen, the center disco booth-style seats began to turn in circles -- culminating with a spritz of fragrance from cleverly concealed plug-in atomizers that hit at the crescendo of the model's ecstasy.

Now that's some drama worthy of a French couture brand.

Alexa Chung and Alexandra Richards spun custom mixes, which can be found and purchased on iTunes. Party-goers were all given $10 iTunes gift cards to snatch up the compilation au gratis.

Hazy purple lighting created a sense of sensuality in the room, and diversions like a tarot card reader and a bevy of iPads laid out to make comments on the whatsyouropium.com blog kept guests curiously entertained throughout the night.

Co-creator of the scent, Honorine Blanc, was also on hand, passionately extolling the virtues of her creation with scent sample cards in hand.

Check out more party photos on WhatIsYourOpium.com, and YSL's Facebook page. Photo: WhatIsYourOpium.com



"Fragrance is about tension. With white flowers like jasmine and lily and a sparkle of mandarin, incense and white pepper, we have achieved that perfectly. It could not be heavy like the original Opium. To be modern is to be light, which is why I used peach and mandarin," Blanc told StyleList.

After four years of agonizing over the details of the fragrance, we wondered: how did Blanc finally know when it was just right?

"Sometimes you feel something in your gut that you can't describe -- like when you meet someone that you love, but you don't know exactly why. That's how I felt when I knew it was done," said Blanc.

As for our thoughts on the juice itself, it's surprisingly on the lighter side -- in spite of a musky amber center that is overtly sexual, yet tempered by the sweet citrus notes of mandarin and peach.

Blanc referred to the scent as a "moist sensuality."

We can only imagine how that translates in French.