Queen Bestows Royal Dukedom on William

As predicted by many, HM the Queen has bestowed the title of Duke of Cambridge upon Prince William. Following her marriage, the bride will be known as HRH Catherine, Duchess of Cambridge.

http://en.wikipedia.org/wiki/Duke_of_Cambridge

http://www.officialroyalwedding2011.org/blog/2011/April/29/Titles-announced-for-Prince-William-and-Catherine-Middleton