Royal-ness.

Kate chose Sarah Burton for McQueen "for its craftsmanship and its respect for traditional workmanship and the technical construction of clothing".  The lace appliqué for the bodice and skirt was hand-made by the Royal School of Needlework.  Individual flowers were hand-cut from lace and hand-engineered onto ivory silk tulle to create an organic design with rose, thistle, daffodil and shamrock motifs. The train is just short of 9 feet. French Chantilly lace was combined with English Cluny lace to be hand-worked in the Carrickmacross needlework tradition. The workers washed their hands every 30 minutes to keep the lace and threads pristine, and the needles were renewed every three hours, to keep them sharp and clean. Fit for a princess.

and just because they're practically royalty...