If it were humanly possible for Grace Kelly and Christie Brinkley to procreate, their spawn might resemble Beth Stern, a refined beauty with mesmerizing eyes and a genuine smile. Looking more West Coast than Pittsburgh, where she grew up, Ms. Stern—né Beth Ostrosky—came to Manhattan in 2000 to pursue a modeling and acting career. Her life changed a year later when she crossed paths with radio personality Howard Stern.