Director Steven Spielberg was joined by Britain's Prince William and his wife Kate, the Duchess of Cambridge, at the U.K. premiere of his new epic "War Horse." The premiere kicked off on Sunday night in London.

Director Steven Spielberg was joined by Britain's Prince William and his wife Kate, the Duchess of Cambridge, at the U.K. premiere of his new epic "War Horse." The premiere kicked off on Sunday night in London.

The premiere was held to benefit "The Foundation of Prince William and Prince Harry." Before the screening, the Duke and Duchess of Cambridge greeted current and former military personnel, as well as Spielberg and cast members.

Based on the best-selling 1982 children's novel written by Michael Morpurgo and adapted into a Tony award-winning play by Nick Stafford, "War Horse" tells the story of the friendship between an English farm boy and his clever horse Joey set against the Great War.

For Spielberg, it was the story of how horses helped in the First World War that first drew him to the project.

Steven Spielberg said, "It was just a very stimulating story for me, almost a romantic story and yet it really, I think, honors the horse and the sacrifices not just everyone made in the First World War, but the millions of horses that were devastated, demolished and it was sort of the end of the horse as a implement of war, the First World War was. All those are reflections that come out in our film."

Speaking on the red carpet, the movie's young star, 22-year-old Jeremy Irvine, admitted he was worried about being upstaged by his four legged co-star. In fact, it was the first film role for the movie's protagonist.

Jeremy Irvine, actor, said, "I was upstaged by a horse in every take. I mean these horses have longer CVs than me. One of the main horses was also Seabiscuit, I mean, they are major movie stars compared to me."

Benedict Cumberbatch was also in awe of the horses in the film.

Benedict Cumberbatch said, "We are just humbled to be around some of the most highly skilled animals of that species. I mean, they really are exceptional these horses and our job is to just deliver a story that is about what they bring to the understanding of what war is."

The "War Horse" kicked off in Hong Kong at the end of last year and it will open in the U.K. this Friday.