Disney mug spoils Oz The Great and Powerful

A Disney merchandise mug appears to have unveiled a spoiler that the film company has been at pains to conceal from forthcoming film 'Oz The Great and Powerful'.

Debate amongst fans over who is to play the Wicked Witch of the West has raged since the announcement of the film's stars, including Rachel Weisz, Mila Kunis and Michelle Williams.

[Related story: Mysterious witch poster emerges for new Oz film]

Disney, meanwhile, had purposely kept the specific casting vague, only confirming that all three would be playing the film's witches.

But now a mug has revealed that Mila Kunis, rather than the previously thought Rachel Weisz, will be playing the film's key villain, the role immortalised by the green-hued Margaret Hamilton in the 1939 film.

This would make Weisz the Wicked Witch of the East, the witch that is killed under Dorothy's house when she arrives in Oz.

There was also some studio misdirection in the official press release, which named Theodora, the Wicked Witch of the West, as 'a beautiful, naïve witch, protected by her powerful sister Evanora'.

The film, which stars James Franco as Oscar Diggs, the man who arrives in Oz claiming to be the prophesied Wizard, is due out in March.

It's been directed by horror legend and ex-Spider-Man helmsman Sam Raimi.