Florence Welch of Florence + The Machine in Her Element Only on Stage

PHOTO: Florence Welch, lead singer of the English indie pop band Florence and the Machine.PlayDonna Svennevik/ABC
WATCH Florence Welch: Old Soul Alive on Stage

Florence Welch of Florence + The Machine performs with an intensity that leaves crowds breathless, but in reality, the 25-year-old singer said she is a shy person, who still feels awkward everywhere but on stage.

"That's an area where I'm comfortable being, or just looked at for sort of what you're doing -- songs," she told "Nightline" anchor Cynthia McFadden. "It makes you feel quite powerful."

Although this British native is the queen of indie rock, Welch penetrated the American mainstream market after her hit song, "Dog Days Are Over," was featured on popular TV shows including "Grey's Anatomy," "Gossip Girl" and "Glee."

But it was not so long ago that Welch was a little girl who would make believe she was a witch, casting spells and playing dress-up at her home in South London. In fact, she still lives in her childhood bedroom at her mother's house.

"I was always singing melancholy songs…in my nightie with a sort of wine glass full of juice, singing along to Billie Holiday," Welch said with a laugh.

Welch, who used to borrow her grandmother and mother's old clothes or wear boyish T-shirts and shorts, has transformed her style into an exotic look. From tight spacesuit costumes to flowy Greek goddess-like dresses, her sometimes bizarre outfits have made her a darling of the fashion world.

And Welch is still coming to terms with her recent, booming success. In January, she made headlines when she partied with Kanye West in New York City. She ended up with a chipped tooth and a ripped dress and set her room at the Bowery Hotel on fire.

"I'm really glad that they let me to still stay because I really love the Bowery," she said.

Since then, Welch said she has sworn off drinking, at least while performing, and while the fire doesn't seem to faze her, the red carpet does. Before attending the Costume Institute Gala at the Metropolitan Museum of Art in New York City -- fashion's biggest night out -- Welch, who donned a lacy Sarah Burton gown with cascading layers, said, "I don't know how people are not just scared on [the red carpet] because everyone is just shouting at you."

"It's like, instead of like stage fright, it's more like life-fright," she added. "The singing stays the same and then the rest of your life becomes something you have to navigate something different everyday."

PHOTOS: Florence Welch's Style Through the Years

Perhaps she pours all of her courage into writing her music -- songs like "Kiss With a Fist," which has a haunting message.

"When I wrote that song, I think I was…it was about being in love and those passionate feelings," Welch said. "Because it didn't feel soft and it didn't feel nice. It felt kind of frightening and it was almost-- I needed to pick images that were as intense as those feelings. But, you know, obviously it was a metaphor."

Welch split from her long-term boyfriend Stuart Hammond last October, but was spotted on vacation with her new beau, James Nesbitt, earlier this year. Wanting to keep that part of her life private, Welch would only say, "he's very nice."

"Nightline" anchor Cynthia McFadden talks with Florence Welch.

Her recent project was writing the theme song for the upcoming film "Snow White and the Huntsman." It's an eerie but powerful ballad called "Breath of Life."

"One of my favorite things I've ever done was recording that song," Welch said. "It's one of those sort of 'pinch yourself' moments."