The event, in London's Leicester Square, was held in aid of the Foundation of Prince William and Prince Harry - the princes' charity.

Some 600 current and ex-members of the military and their families were there, along with Spielberg and cast members.

The equine star of the film - Joey the horse - also walked the red carpet.

Spielberg said it was a "very prestigious" honour to have a royal premiere. It was held on the eve of the duchess's 30th birthday.

The film's cast includes Sherlock actor Benedict Cumberbatch, Emily Watson, Tom Hiddleston and newcomer Jeremy Irvine.

Spielberg said it was an "honour" for the royal couple to take part in the premiere.
"This is my first royal premiere for the Duke and Duchess, having done them before for the Queen and the Queen Mother. This is a wonderful occasion tonight. This is so exciting. I get a buzz."

Actor Jeremy Irvine said: "I am a little bit overwhelmed. It feels like a long way from home."

The movie is adapted from Michael Morpurgo's 1982 novel about a boy who tries to track down his beloved horse that has been shipped to France to serve in World War I.

Tom Hiddleston, who plays Captain Nicholls in the film, paid tribute to the royals. "It's a huge privilege that the film has been blessed by them and they decided to lend their support behind it."

It follows a theatrical production, which opened at the National Theatre to rave reviews in 2007.

bbc.com