Royal Households and Data Protection Registration
The Prince of Wales website lists the following Royal Households, I have cross-referenced this list of the public register of Data Controllers held by the ICO:
(believe it or not there is an order of precedence for the Households, they are listed here in that order)
Household of The Queen - (see register entry for Keeper of the Privy Purse)
Household of The Prince Philip, Duke of Edinburgh
Household of The Prince of Wales and The Duchess of Cornwall
Household of His Royal Highness Prince William of Wales and His Royal Highness Prince Henry of Wales - no separate registration - some facilities are shared ...