Kristen Stewart is embarrassed by her "pinhead" when she donned a suit of armour for 'Snow White and the Huntsman'.

The 21-year-old actress appears as the titular fairytale character in the forthcoming movie, which also stars Charlize Theron as the evil queen and Chris Hemsworth as the hunter, and she admits the costume she had to wear left her feeling "strong" but concerned about her small frame.

She said: "It's not a little girl sitting by a well with little tweety birds telling her what to do and where to go.

"The costume makes you feel kind of strong occasionally, sometimes, but I feel kind of tiny, my pinhead sticks out of these enormous things!"

Oscar-winning actress Charlize also revealed she thinks of her character as a "serial killer", but believes the reason the queen is so evil is due to her "circumstances".

She said at the San Diego Comic-Con Festival: "This, as a fable, she sort of just starts off as a bad person, so it was important to understand why she is the way she is.

"A lot of her circumstances will kind of bleed into her actions. She's a serial killer. I'm pretty much preparing to play a serial killer."

'Snow White and the Huntsman' is due for release in 2012.