The Duchess of Cambridge was moved to tears by the First World War epic War Horse at its premiere, according to the film's director Steven Spielberg.

Kate, who shared the red carpet at Sunday night’s event in London with the film’s equine star, stole the show in an elegant floor-length black lace evening gown by Somerset’s Alice Temperley.

Spielberg, who named Dartmoor, one of the film’s locations, as a “star” of the movie, told BBC Breakfast he believed the Duchess needed to wipe her eyes as she watched the film.

“I was sitting next to her and all I know is at one point my wife, who was sitting to my right, right in front of my face she passed a Kleenex ... I saw the Kleenex go across my face, arrive and stop but I didn’t want to intrude on her experience watching War Horse so I never glanced over.”

The event was also attended by 600 serving and ex-serving military personnel and their families as well as beneficiaries of military charities.

Kate, who celebrated her 30th birthday yesterday, attended the premiere in Leicester Square with the Duke of Cambridge.

The royal couple met servicemen and women as well as the cast and crew and chatted animatedly with Spielberg, Sherlock actor Benedict Cumberbatch, Emily Watson and Tom Hiddleston, who plays Captain Nicholls and went to school with William.

The royal couple went to the event in aid of the Foundation of Prince William and Prince Harry, which helps the welfare of those in the armed forces.

The filmmaker, who said he did not believe he had made “a war movie”, admitted he shed tears the first time he saw the play which inspired the film.

He said: “The play did that to me, I came out of the play a soaking wet wreck.”

Spielberg, whose films include Saving Private Ryan, Jaws and Raiders Of The Lost Ark, said he had been impressed by the landscape in Dartmoor where some of the film was shot.

He said: “There’s no place like it in the world. When I got to Dartmoor I realised I had a third character that I had to include in War Horse and that was the land and the sky so Dartmoor plays a major role.”

The film, which was nominated for best drama at the Golden Globes, follows on from the success of the play, which debuted at the National Theatre in London in 2007 before sell-out West End and Broadway runs.

It is based on the children’s book War Horse, written in 1982 by Devon-based Michael Morpurgo. The novel tells the story of a boy called Albert and his horse, Joey, who is sent to fight in the Great War.

Praise from the critics for the West-based blockbuster

Steven Spielberg’s epic big-screen adaptation of War Horse was largely greeted with a thumbs-up from the newspaper critics.

The film was awarded four out of five stars in both The Times and the Daily Express, while the Independent gave it three.

Writing in The Times, Kate Muir warned filmgoers it was “impossible to hold back the floods”, admitting she teared up seven times and cried twice while watching it.

Michael Morpurgo’s 1982 novel, about a farm boy whose beloved horse is sold off to the Army, was later turned into a hit play with wooden puppets that wowed audiences.

Ms Muir noted the “astounding” action cinematography of the movie version, adding: “Steven Spielberg has turned the spare, minimalist play of War Horse into a sweeping schmaltzy epic movie, but its power is undeniable.”

She said the film, like Morpurgo’s novel, makes the First World War “palatable” for older children, but warned that for younger children the “terror levels” of Spielberg’s Saving Private Ryan sometimes seep through.

But she was full of praise for the equine star – played by several horses – adding: “The ensemble best-of-British cast cannot touch the drama of Joey flashing the whites of his eyes, rearing in terror and galloping across the no-man’s land of the Somme; trailing barbed wire through the battleground.”

In the Express, Alan Hunter described Spielberg’s latest war movie as “a touching saga of courage, loyalty and the truest of friendships”.

He said the director cannot compete with the “theatrical intensity” of the stage show, but instead embraces the story’s traditional virtues “with all his heart and craft”.

“There is not a hint of cynicism in this sweeping, sentimental big screen epic that happily trots in the footsteps of past masters like John Ford and David Lean,” Mr Hunter wrote.

Although he said the film was “unavoidably episodic” and was slowed down by one long sequence in particular, he said these were “minor quibbles in a bravura display of Spielberg’s command of the film”. However, Kaleem Aftab, for the Independent, was less glowing in his review.

In abandoning the acclaimed puppets from the stage production, he said Spielberg “adds realism but loses some of the magic”.

Mr Aftab said some sentimentality was inevitable, but added: “The thin line between sentimentality and schmaltz is all too often crossed.”

WMN opinion: War Horse can be a winner for Dartmoor tourism too

Royal triumph on red carpet for Michael Morpurgo's War Horse film