The Duke and Duchess of Cambridge, William and Kate, shelter from the rain as they arrive for the royal film premiere of War Horse

The Duchess of Cambridge spent the eve of her 30th birthday attending the War Horse film premiere in London with husband William.

The Duchess of Cambridge arriving for the UK premiere of War Horse, at the Odeon Leicester Square

Kate graced the red carpet wearing a floor-length black lace gown by Alice Temperley.

The long-sleeved dress, which was nipped in at the waist, was accessorised with a black clutch bag and intricate diamond jewellery.

William and Kate shared the red carpet with the star of the film - a thoroughbred called Joey, who was driven from his stables in Milton Keynes to face fans and photographers.

The royal couple walked up the red carpet, sheltered from the rain by a see-through umbrella, and when Kate spotted the horse she grinned broadly.

War Horse is the film based on the play which was inspired by Michael Morpurgo’s novel

Mr Morpurgo said it was an “honour” the Duchess chose War Horse as her first royal premiere and said he would send her a copy of the book as a birthday gift.

“She is a wonderful example of dignity and calm and I like that in her,” he said.

The Leicester Square premiere of Steven Spielberg’s film was also attended by 600 serving and ex-serving military personnel and their families, as well as beneficiaries of military charities.

The royal couple went to the event in aid of the Foundation of Prince William and Prince Harry.

Spielberg said it was an “honour” to have William and Kate in attendance.

The director said: “This is my first royal premiere for the Duke and Duchess, having done them before for the Queen and the Queen Mother.

“This is so exciting. I get a buzz. You never grow out of something like this.”