Variety have confirmed that both Alfred Molina (Doc Ock in Spider-man 2) and oscar winning Ben Kingsley shall be a part of the Prince of Persia movie:

Molina will play Sheik Amar, who becomes a mentor to the prince.
Shooting is slated to begin in July in the U.K. and Morocco.

Variety later confirmed that Kingsley shall be playing the villain Nizam,

In the fantasy actioner, Kingsley portrays Nizam, who plots to kill his brother King Shahrman and blame it on Prince Dastan so he can take the throne.

Thanks hobo123