Her friends and family are planning a low-key 30th Birthday celebration on Monday.
But the evening before was all about high-octane glamour for Duchess of Cambridge who was radiant in sweeping floor length cream gown embroidered with delicate black flowers at her first royal premiere.
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Accompanied by Prince William, she dazzled on the red carpet at the UK screening of Steven Spielberg's new film, War Horse.
As Kate stepped out on to the red carpet in the lacy creation by Alice Temperley, the creator of her sister Pippa Middleton's emerald dress for the evening of the royal royal wedding, it began to drizzle.
Luckily, the gallant Prince was prepared with a trusty umbrella to shield his wife.
The event was a benefit for the foundation established in the name of the future King and his brother.
Waiting crowds were thrilled to see the glamorous royal couple, and their enthusiasm was reflected by the flick's heavyweight director.
"This is so exciting. I get a buzz. You never grow out of something like this," said Steven.
"It's an honour 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".
The film recounts the story of young man who bonds with a horse sold to the British cavalry during World War I.
Its stellar includes Emily Watson, and Benedict Cumberbatch who plays Sherlock Holmes in the BBC One series. ;
Emily gave away anecdotes of her brush with the newest member of the royal family, revealing she had: "been told to address her as 'Ma'am' as in 'jam'"
War Horse opens in cinemas on Friday January 13.
Catherine at 30: A woman with the world at her feet