Roland Mouret cream slit gown

On May 8, 2012 the Duke and Duchess of Cambridge arrived at for a dinner in William's honor at the Thirty Club at The Claridges Hotel.  Kate wore a cream Roland Mouret gown.  Despite a high neckline and long sleeves, the modesty was contrasted by a thigh high slit and Jimmy Choo platform stiletto sandals.

Via - StyleBistro.

Via - InStyle. 

Via - William and Catherine Tumblr.

I found this Bisou Bisou long sleeve dress available at JC Penney.  With its round neckline, long length sleeves, and high slit, this version definitely resembles Kate's, although unfortunately only comes in black.

Strangely it seems to be unavailable on the website right now.  Maybe its a black Friday thing because I still saw it in-store today, but you can check out the line of Bisou Bisou dresses here.

Bisou Bisou at JC Penny - long sleeve dress.