The festival has teamed up with Vodafone's Centre Stage to host the official dress-up day on Sunday, August 3.
The inaugural theme is everything Kings and Queens, so festival-goers can express their interpretation of a modern day royal.
Get your thinking cap on for costume ideas, which could be inspired by Kings, Queens, Princes, Princesses, tiaras, crowns and Marie Antoinette.
The Vodafone Centre Stage also will have a Dress-Up Room where you can purchase a regal number.
The day will conclude with a royal Coronation ceremony for the best King and Queen, who will each win a Golden Ticket pass for the Centre Stage 2015 festival line-up, a Vodafone handset and VIP camping at Castlepalooza 2015.