The Duke and Duchess of Cambridge are set to make their Royal Ascot debut as a special favor to Queen Elizabeth II in honor of her birthday, according to a report.

Prince William and wife Kate Middleton will be joining the Queen, as well as other members of the royal family, on Wednesday for the Royal Meeting at the Ascot held in Berkshire. The annual race meeting has been an event that Queen Elizabeth II has attended diligently over the past decades. The royal monarch was said to have previously extended invitations for the royal couple to join her at the Royal Enclosure during previous years’ celebrations. However, it was only now that the Duke and Duchess of Cambridge have decided to attend as a “birthday surprise” for Queen Elizabeth II, Vanity Fair magazine reported.

A source told Vanity Fair that Prince William and Kate will be at the Royal Ascot especially since the event means so much to the Queen. “They will be there for one day this week. They will enjoy an afternoon in the royal box with Her Majesty,” the source added.

Royal fans and fashion lovers can also look forward to seeing the Duchess of Cambridge wear another stylish fashion ensemble given the event’s formal daywear dress code. Ladies attending the event are also required to wear a hat or a headpiece provided it meets the specific size. Fascinators are also not allowed, as indicated in the same report. For the gentlemen, male attendees are expected to wear a top hat, black shoes, a waistcoat, as well as a tie.

The 2016 Royal Meeting at the Ascot started on Tuesday, June 14, where Prince Harry, Prince Charles, the Duchess of Cornwall, the Duke of York and Queen Elizabeth II all arrived to witness the first-day festivities of the annual race meeting, Royal Central reported.

On Wednesday, Prince William and Kate will witness the mile long group 2 horse race. The said race was renamed as The Duke of Cambridge Stakes in honor of Prince William on 2013.