Looks like Kenneth Branagh is well on his way to a full complement of stars for his Cinderella.
Stellan Skarsgard... is being lined up to play "the grand duke, the king’s adviser, who just may have ulterior motives in his guidance."(By the way - this means, he's "in talks" - not that he's confirmed as a cast member. Yet.)
We will see Skarsgard next in his role as Dr. Erik Selvig (for the third time) in Thor: The Dark World, being released in November 2013.
Sources: The Hollywood Reporter, ComicBookMovie.com