It's one thing dressing for the red carpet but what does a girl wear when she's invited to a party thrown by Prince William at Windsor Castle?
Emma Watson made a good case for wearing a plain white shirt as she arrived at the event to celebrate the work of the Royal Marsden Hospital.
Many of the guests, including Emma, were dressed in pieces by designer Ralph Lauren, who is funding a breast cancer centre at the hospital.
She tucked her shirt into a floor-sweeping grey skirt which she accessorised with a matching box clutch and silver necklace.The best part of Emma's look? It had to be her berry-red lipstick and her swept-back updo.
Kate Moss also looked stunning in this black and sheer dress paired with sandals and drop diamond earrings.