To the world, Louis Armstrong is iconic-a symbol of musical genius, unparalleled success and unassailable character. To Sharon Preston Folta, he was, simply, Dad. Despite the enduring celebration and study of Armstrong's life and career, no one, save for close family and friends, knows Sharon exists. Even in the trumpeter's death she remains Armstrong's secret-the product of a two-decade-long affair between the long-married musician, and the vaudeville dancer Lucille Preston. And for more than half a century, she has lived her life hiding in the shadows of her father's fame. Until now. Now,...