It's widely expected that the Duchess will be walking the red carpet with her husband at the London premiere of Stephen Spielberg's War Horse on Sunday night, with the party taking place afterwards.
Here's hoping Kate doesn't read the press. Otherwise this party won't be much of a surprise...
See our pick of the birthday girl's perfect 10 style moments:
Suggested For You
Get top stories and blog posts emailed to me each day. Newsletters may offer personalized content or advertisements. Learn more