Intentional or not, it’s something that shouldn’t have happened. Even if it was an oversight, should that be the case, someone should have caught this. That is, young William, why you use the resources available to you when tailoring a guest list. People who’ve done this for a couple of decades already usually know which way is up.
Correction: I have since been informed, thank you Marlene, that The Telegraph got it wrong and King Juan Carlos simply passed his invitation on (as he hardly ever attends weddings, we knew that).
Trouble is, and there I remain standing with my criticism, it’s been said that two invitations were sent to each of the royal houses. Now there’s a few cases (Spain, The Netherlands) where we always have a threesome doing these events, the Queen, the heir and the heir’s spouse (in the case of Spain because Juan Carlos doesn’t do these events, in the case of The Netherlands because Queen Beatrix is a widow). It would have been a good idea to consider this from the get-go, especially since the state visit Charles and Camilla conducted to Spain certainly wasn’t a spontaneous outing to visit friends across the channel.