Steven Spielberg didn't want to "intrude" when Britain's Duchess of Cambridge began crying while watching War Horse.

Catherine and her husband Britain's Prince William attended the UK premiere of Steven's latest film at London's Leicester Square last night.

Steven was delighted that the royals came to the event. He was even more stunned when he realised Catherine who turns 30 today - had become tearful while watching the heartfelt drama.

"I was sitting next to her. All I know is that my wife passed a Kleenex over," he smiled in an interview with BBC Breakfast.

"I didn't want to intrude on her experience so I didn't glance over. My peripheral vision tells me that she was moved by the film."

The event was held in aid of the Foundation of Prince William and Prince Harry - which recognises the welfare of those who serve their country in the British Armed Forces

The foundation works with the Forces in Mind Trust to help former military personnel adjust to life outside of the forces.

The premiere is expected to raise approximately 300,000 for the charity, with 30 people paying 10,000 to attend the prestigious red-carpet event.

Alongside the celebrity personalities, cast and crew gracing the red carpet - 30 servicemen and women from each of the regiments Prince William is involved with attended the screening.

They were all dressed smartly in their military uniforms.