"It takes a lot of guts. I'm really a shy person," the singer tells the magazine. "But in my everyday world, as a musical performer, I'm playing a character. I had to tap that same character."
Making the SI cover for the annual top-selling issue propels the singer into an elite class of model whose ranks include Christie Brinkley, Elle Macpherson, Rachel Hunter, Heidi Klum and Tyra Banks.
See Beyoncé's Photos
Though the 25-year-old singer has been asked to pose in a swimsuit before, her mother says she wanted to wait for the right time. "At every shoot," Tina Knowles says of her much-photographed daughter, "they always bring some swimsuits and ask, 'Can we shoot in this?' It's always been 'No! When it's time to do swimsuits, it's going to be something big."
It doesn't get bigger than the coveted cover of SI.
To physically prepare for the shoot, the "Bootylicious" singer says she had to watch what she ate – which was especially tough because it was scheduled right after Thanksgiving. "At dinner, I kept thinking: this extra piece of pie will show up," she says. "I always make sure I celebrate it up, but I was so terrified with every little thing I ate this year."
Before the photo session, the singer relaxed by listening to some of her favorite music. "I listened to John Legend's new album. It's soothing, sexy and old school. It got me in the mood."
And once it got started, Beyoncé had a little help from her friends – and most of her family. "Kelly Rowland (of Destiny's Child) showed up. My mom was there; my nephew," she says. "Dad was going to come, but he said, 'Well, I'll, um, meet you in Orlando after the shoot. I'm not so sure that I want to see this. All my blessings; you're a big girl. But I'm not so sure I want to see it.' "
But dad had nothing to worry about. Beyoncé says she's proud of the pictures. "These are photos I can show my kids some day," she says, "so I can say, 'See, momma was beautiful. Look how good I looked!' "
To see all the Beyoncé pics and more, go to SI.com.