The Casino Royale star will play the sorceress Morgan in the fantasy drama, which also stars Joseph Fiennes and Jamie Campbell-Bower.
"I was worried at the beginning that she is evil and that's it," admitted Green. "But she's a very rich character. And she wants to be a great queen. She believes in equality between men and women. She celebrates sexuality, nature, life."
The actress added that Morgan's rivalry with the young Prince Arthur (Campbell-Bower) "will evolve" as the series continues.
"She hates him at the beginning," she confirmed. "But her head is telling her 'I hate him' while her heart is telling her otherwise."
Green also admitted that she is frequently attracted to "extreme, intense roles" such as her Camelot character.
"There's always something wrong with my characters," she laughed.
Camelot premieres on April 1 on Starz.
> Eva Green: 'Camelot will be sexy'