Prince William and Kate attend the War Horse premiere in London
01/09/2012 AT 11:40 AM EST
The Duchess of Cambridge
is renowned for her poise and grace. But she needed some assistance – from none other than Steven Spielberg's wife – at a crucial moment of the War Horse premiere
Sunday in London.
Spielberg has revealed that his wife, actress Kate Capshaw, was passing tissues to Kate, who turned 30 on Monday, as the film's story hit a particularly moving section.
Asked if Kate was in a "right state," he told the BBC
on Monday that he was sitting between the duchess and his wife. "At one point my wife, who was sitting to my right ... passed a Kleenex to the Duchess of Cambridge. I just saw the Kleenex going across my face."
In his "peripheral vision" he witnessed the royal eyes being dabbed, "but I didn't want to intrude on her experience of watching War Horse
so I never glanced over."
Kate and her husband, Prince William
, hosted a reception afterward for special guests and the movie's cast at the Queen's Gallery at Buckingham Palace, and raised several hundred thousand dollars for the Foundation of Prince William and Prince Harry.
For screenwriter Richard Curtis, it was a thrill to have the couple at the premiere. "I love them. We have to thank them for such a happy year last year," he told PEOPLE.
Adding to the excitement was a cameo by Joey the horse at the premiere. "I will always try to write a horse into my movies now, so as to have a horse on the red carpet," Curtis said.
Added actor Jeremy Irvine, one of the film's stars: "It's lovely to see Joey again. He's my date actually tonight. It's the best I can do."