The Sports Illustrated swimsuit issue cover was officially unveiled last night on the Late Show With David Letterman, but some people got a sneak peek via Twitter. Rana Wardlaw tweeted a picture of the Irina Shayk cover yesterday, and she explains: "I saw it from my office window," the Huffington Post reports. "They unveiled the billboard for a few minutes to tape it for the Letterman show and then covered it back up. I guess they didn't cover it fast enough!" Shayk, a 25-year-old Russian model, is dating soccer star Cristiano Ronaldo. (The AP has since obtained the photo, see both in the gallery.)