Happy birthday, Kate Middleton! Take a look back at her royal transformation

Happy birthday, Kate!

The mom to Prince George, Princess Charlotte and Prince Louis turns 37 on January 9th -- and we're celebrating by taking a look back at her transformation from Prince William's girlfriend to duchess.

There's no doubt that the Duchess of Cambridge is the style icon of our generation. While she often opts for high-fashion British designers such as Alexander McQueen and Jenny Packham, Kate is also known to favor more affordable brands such as Zara and Topshop. And no matter the price tag, she's continued to dazzle with her sartorial choices.

From red carpets to charity events to royal weddings, her style transformation is truly fit for a princess: