It's official: Britney Spears is going to have a baby, one more time. Is it too early as Sean Preston's ( her first baby) will be celebrating his first birthday only few weeks before his brother/ sister comes to life. After months of speculation about the size and shape of her abdomen, the pop star confirmed to David Letterman Tuesday that she is expecting her second child with her aspiring rapper husband, Kevin Federline. Spears, who was in New York this week promoting the latest scent in her fragrance line, made a surprise Late Show appearance to break the news. "Don't worry Dave, it's not yours," she said. Spears was accompanied by eight-month-old Sean Preston, whose September 2005 birth was notably memorialized by the sculpture Monument to Pro-Life: The Birth of Sean Preston, one artist's interpretation of Spears expelling her firstborn into the world. For those keeping track at home, Sean Preston's baby brother or sister will make the fourth child