Is there already something known about the guest list?
I fear that nearly no foreign royal persons (CP and CPss of the other European countries) will be there. The Windsors seem to have a strange relationship to other royal houses. They are not linked closely to the other royals. So nobody of them was at Prince Charles and Camilla's wedding. Prince Charles, Camilla, William and Harry were not at Victoria's wedding. William was hardly ever asked to be godparent of a royal baby. (He is only godfather of Constantine Alexios - as far as i know).
I also remember something about this holiday on Mallorca over 20 years ago - something about Diana flirting with Juan Carlos. The holiday ended in a bad atmosphere.
And William and Catherine want the wedding to be private. At least to the dinner and dancing in the evening the other royals are not invited. (Quote (announced yesterday): "The Prince of Wales will give a private dinner, followed by dancing, at Buckingham Palace in the evening, for the couple and their close friends and family.").