Sienna Miller and Sam Worthington sit down with “Extra’s” Billy Bush to talk “Horizon: An American Saga,” Kevin Costner’s epic new multi-volume Western. Sienna spoke about getting the call from Kevin to do the project and her love for the genre, while Sam confessed he couldn’t believe it was real. The two also spoke about how their characters are “star-crossed” in their romantic relationship. Sienna also recently made an epic appearance in “Curb Your Enthusiasm,” and she explained how that came about. Plus, she dished on new mom life after recently welcoming her second child, who is now six months old. The first chapter of “Horizon” hits theaters June 28.