Their Royal Highnesses Prince Edward and the Countess of Wessex are due at Chichester Cathedral Festival of Flowers later as part of the Queen's Diamond Jubilee celebrations.
The couple will be welcomed to the event by the Dean of Chichester Cathedral, the Very Reverend Nicholas Frayling.
A Royal visit is always a great encouragement, and we are delighted that the Festival of Flowers is to be honoured in this way. I am sure that Prince Edward and the Countess will have a memorable visit, along with the many thousands who will be attending during the course of the festival."
The Festival of Flowers will remain open during and after the visit, although numbers inside the cathedral may need to be restricted a little at times. Well-wishers who would like to see the Royal party can gather outside the cathedral at the front by the St Richard statue.
Entry into the cathedral may be limited during the afternoon, due to the Royal visit, but it will remain open until 7pm.
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Two private citizens have already paid a "significant deposit" to take the week-long trip.