Carolina Herrera recalled how the 21-year-old transformed from an actress modelling a costume to a bride when she donned Bella Swan's satin gown.
"We did three fittings. When she initially put on the dress and looked over her shoulder into the mirror, she was very moved," Herrera told People.
"In that moment she was not an actress or a character in a film but instead a bride, and a happy one at that."
Explaining her thought process behind the dress design, Herrera added: "I took into consideration the character of Bella and Kristen's portrayal of her, and what this fantasy character would choose to wear for the most important day of her life.
"It's very romantic, and when all the details come together, it creates a vision specific to Bella's style and personality."
Stewart previously admitted that her screen wedding to real-life boyfriend Robert Pattinson in Breaking Dawn - Part 1 felt like "a genuine experience".
Bella's dress normally retails for $35,000 (£22,600), though a replica was recently made available in the US for just $799 (£517).
Watch the trailer for The Twilight Saga: Breaking Dawn - Part 1 below: