FYI: It was designed by Sarah Burton.

Sources:
http://windsorknot.today.com/_news/2011/04/29/6554229-finally-kates-royal-wedding-gown-revealed

http://www.thesun.co.uk/sol/homepage/news/royalwedding/3554698/Designer-thought-to-be-responsible-for-Kate-Middletons-dress-seen-running-into-Goring-hotel.html