The actress marries her on-screen beau Edward Cullen, played by her real-life man Robert Pattinson, in the final installment of the vampire saga, due out later this year.
And she has revealed that trying to keep the dress under wraps was like a military operation.
'The wedding was filmed Secret Service style insane,' she told People magazine.
'The crew was completely inconvenienced. There was no cell phone or email. I said thank you so much because if this dress gets on the Internet, I'll die!
'I had to be locked into the dress to protect it.'
And she admitted that she was just as jittery on the day as she would have been for the real thing.
'When I got to set I was as nervous and terrified as I expected myself to be,' she said. 'It was beautiful.'