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The Kate Effect strikes again! Catherine, Duchess of Cambridge wore a blue tweed Rebecca Taylor suit yesterday, and the $450 jacket sold out within hours. And the New Zealand-born, New York designer is thrilled: “A lot of our similar suits sold out, too,” Taylor told InStyle.com exclusively. While the designer has no plans yet to recreate the exact outfit, she will sell similar sets next season. “It’s the same idea. We always have skirt suits,” she said of her fall offerings. And the Duchess has caused sales boosts before—see more items that flew off shelves due to the royal in the gallery.

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For some extra tips on picking the perfect holiday outfit, we turned those who know best—celebrities, stylists, and designers. Find out what Emmy Rossum, Emma Roberts, Rebecca Taylor, and more have to say about their favorite party-ready looks in the gallery now.

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Rebecca Taylor’s spring 2012 runway show offered her signature feminine vibe, with an added sporty twist. Army jackets topped flowing silk skirts and anoraks covered ethereal dresses, giving the collection a pretty-with-a-tomboy-edge effortlessly cool quality. Citrus tones like limeade and citron brightened up the otherwise mostly-neutral palette, especially for the accessories, where structured bags came in bubblegum pink with shots of metallic. The footwear had a touch of ‘40s flair with modern updates, like a leopard-print heel or color-blocking. See our favorite looks from the Rebecca Taylor show in the gallery.

MORE: Designers Sketch Their Inspirations!

— Violet Gaynor

Backstage at the Rebecca Taylor fashion show today, Michelle Tractenberg exclusively revealed to InStyle that she’s planning to create a capsule collection with the designer. “It’s a ways away, but we’re conceptualizing,” said Tractenberg, wearing a Rebecca Taylor sweater and jacket and an Erickson Beamon necklace. “We’ve  been talking closely about what makes a girl a girl and a woman a woman and what definitive moments in a woman’s life can be like articulated in a woman’s outfit. It’ll be very ladylike for those different moments and occasions we all have.” Therefore, the actress has been spending lots of time in Taylor’s showroom. “I guess it’s surreal that I’m good friends with designers whose work I really admire and love,” she said. We can’t wait to see their upcoming collection!

MORE: See front row photos at Fashion Week!

— Nakisha Williams