On Sunday, the Duke and Duchess attended the star-studded UK premiere of Stephen Spielberg's "War Horse." Despite the rain, Kate wowed the crowds in London's Leicester Square in a black lace Alice Temperley gown -- accessorized with an umbrella, courtesy of her husband.
But Monday's festivities look set to be much quieter -- a St James's Palace spokesperson told CNN it would be an ordinary day for the Duke and Duchess, with any celebrations likely to be "private and low-key".
Her 30th birthday comes in the wake of a landmark year for Kate: The past 12 months have seen her take on her first royal engagements and marry into the monarchy in a ceremony watched by millions of people around the world.
Just weeks after the wedding, Kate and Prince William were greeted like rock stars when they took part in their first overseas tour together, visiting Canada and the United States. This year there are likely to be similar levels of excitement when the couple travels to Malaysia, Singapore, the Solomon Islands and Tuvalu, as part of the celebrations for the Queen's Diamond Jubilee.
And there is already fevered speculation as to whether the Duke and Duchess will welcome their own new addition to the royal family in the months to come.
