The Twilight star made the comment in an interview with Balenciaga creative director Nicolas Ghesquière for Marie Claire.
"I'm a miserable c**t," she said.
"I'm not sure if I'm most happy when I'm comfortable and content or when I'm pushing myself to the limits. There are such different versions of happy. And I really appreciate both."
Recent rumours have suggested that Stewart has reunited with her Twilight co-star Robert Pattinson after it emerged earlier this year that she had cheated on him with director Rupert Sanders.
However, reports have now claimed that the duo will not be appearing together in the initial round of promotion for Twilight: Breaking Dawn - Part 2.
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