Kate Middleton is set for a "low-key and private" 30th birthday today (09.01.12).

Buckingham Palace officials revealed the Duchess of Cambridge - who tied the knot with Britain's Prince William in April 2011 - will have a toned down Celebration after appearing at the premiere of Steven Spielberg's 'War Horse' movie alongside her husband last night (08.01.12).

The duchess wore a stunning floor-length black lace gown by Alice Temperley as she and the prince stunned onlookers by walking down the red carpet at the event in London's Leicester Square in aid of The Foundation of Prince William and Prince Harry.

And Steven admitted he was "delighted" the pair were able to attended the premiere.

She said: "I'm delighted to be here with the royals. This is my first royal premiere for the duke and duchess, having done them before for the queen and the Queen Mother.

"This is a wonderful occasion tonight. This is so exciting. I get a buzz. You never grow out of something like this."