The actress turned 21 in April (11) and her big day coincided with a bash to mark the end of The Twilight Saga: Breaking Dawn Part 2 shoot.
However, rather than revel in the attention, Stewart attempted to downplay her birthday - but her co-stars had a surprise ready for her.
Actress Julia Jones tells E! Online, ""There was a huge cake for her, but she didn't want it to be about her birthday; she wanted it to be about the wrap party. So they didn't bring it out.
""At a certain point, myself and a few other people were like, 'Wait a minute. Where is Kristen's cake?' We went back into the kitchen and demanded they bring the cake out. It was quite a scene.
""She was totally fine (about the celebration) but I understand, because the wrap party was a big deal. I'm very shy about my birthday also. You don't want any more attention.""