The actress, who previously described Bella and Edward (Robert Pattinson)'s union as "important", revealed that the elaborate Carolina Herrera gown designed for the scene made it come to life.
"Nobody saw it until I walked out, which made me so... It wasn't about the dress; it was just everything involved. I was like, ugh, so very the centre of attention at that very moment," Stewart explained during the MTV First: Twilight live stream.
"[Rob] saw it before. And I was like, 'No, you can't.' It did feel, like, very sort of realistically ceremonial. It was very, very emotional for me."
The Twilight Saga: Breaking Dawn - Part 1 is released in cinemas worldwide from November 18.
Twilight director Bill Condon recently praised Stewart's performance in the final film, promising that she would "surprise" fans of the series and critics alike.
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Watch a trailer for The Twilight Saga: Breaking Dawn - Part 1 below: