Kevin Costner is opening up about leaving 'Yellowstone' and revealing why now was the right time to confirm his departure. While promoting the forthcoming first movie in his Western film series 'Horizon: An American Saga,' the actor and director told The Hollywood Reporter's Tiffany Taylor why he finally made the official announcement last Thursday that he would not be returning as 'Yellowstone' patriarch John Dutton when the hit Paramount Network series returns for its final episodes on Nov. 10.