The Duke and Duchess of Cambridge attend the War Horse premiere in London

By Simon Perry
Updated January 08, 2012 02:30 PM
Tim Whitby/Getty

Although royal aides say she’s planning a “low-key” celebration of her 30th birthday on Monday, the Duchess of Cambridge was all glammed up for her final night as a 20-something.

Kate, in lacy floor-length gown by Alice Temperley and her own jewels, joined husband Prince William at her first royal film premiere – for War Horse – in London’s West End.

Just before their arrival, a drizzle started to fall, forcing William to hold an umbrella above them for their red carpet stroll.

The event benefited the Foundation of Prince William and Prince Harry, which has just announced plans to support a trust set up to help military servicemen and women transition back into civilian life.

The royal newlyweds greeted director Steven Spielberg and the cast and crew of War Horse, including the film’s lead actor, Jeremy Irvine.

“The fact that they’re here to watch my fat face on a cinema screen is bizarre,” Irvine said. “It’s such a thrill. And also for their charity. It’s a great cause.”

William and Kate, who will host a reception at the Queen’s Gallery at Buckingham Palace after the premiere, weren’t the only ones turning heads at the event.

“Joey” the horse also left his indelible mark on the red carpet.