By StyleWatch
Updated December 20, 2010 06:00 PM

Mark Cuthbert/Press Association Images/Abaca

Kate Middleton gave her blessing to another designer Saturday when she attended her first official outing with Prince William since the engagement. The princess-to-be strolled confidently into the charity gala event to aid Teenage Cancer Trust in a cream and black silk chiffon ‘Titan’ dress by British designer Alice Temperley, showing off its beaded decorative collar, but hiding the three-quarter length puffed sleeves under a fitted black jacket. “The dress has a very flattering cut,” a spokesperson for the designer told PEOPLE, adding, “I’m not sure where she got it. She must have bought it.” Temperley, who is known for her elegant, feminine designs, has three stand alone boutiques in London, L.A. and N.Y.C., but fashionistas won’t be able to buy into this look of Kate’s: the £895 ($1393) dress, from the Temperley London’s fall 2009 collection, has completely sold out. –Liz Corcoran

Courtesy Temperley London