The actress, 26, is on the cover of Vogue magazine's August 2014 issue.
Talking to the magazine, Lively said that when Florence Welch was singing at her wedding reception, sparklers were brought out. One of them burned the front of her custom-made Marchesa gown.
"And later, my dress was hanging up and Ryan said, 'Isn't that beautiful?' I said, 'What?' And he pointed to the burn. My heart just stopped, because it was such a sensitive little subject. And he said, 'You'll always remember that moment with Florence singing and the sparklers. You have that forever, right there, preserved'. Now that's my favorite part of the dress," the 'Gossip Girl' star said.