Happy 4th birthday, Vivienne Marcheline and Knox Leon!  Brad Pitt and Angelina Jolie's twins are celebrating their birthday today, so OK! decided to share some of their best photos with you! Can you believe Vivy and Knox are already 4 years old?  OK! GALLERY: ANGELINA JOLIE TAKES PAX, ZAHARA & VIVIENNE FOR A STROLL IN NEW ORLEANS!  "I have a great, great partner; he's the best daddy, and we have fun!" ... Read More >>