And that's led to suggestions, even among monarchists, that his heir, Crown Prince Felipe and his wife Letizia take over the throne.

CNN: Will any of Europe's other older royals step down?

Other royal guests included Prince Pavlos of Greece and Princess Marie-Chantal, Queen Sofia of Spain, Prince Felipe and Princess Letizia of Spain.

BBC: Royal wedding: William greets fans ahead of wedding

They show Prince Felipe and his bride standing together, confidently smiling.

BBC: NEWS | Europe | Spain revels in feel-good wedding

Two months ago, Spain's Prince Felipe broke off a relationship.

ECONOMIST: They just won't fold up their beds and slip away

But lately and for the first time, discontent with the monarchy has spread beyond right-wing parties, and politicians have openly called for him to abdicate in favor of his son, Prince Felipe.

FORBES: Bad Timing for a Royal Spanish Scandal

In Spain, the declining health of the 75-year-old monarch and recent financial scandals that have tainted the monarchy have intensified calls for him to abdicate in favor of Crown Prince Felipe, his 45-year-old son.

WSJ: An Austere Coronation for New Dutch King

The ceremonies will be attended by other invited royals and high-ranking dignitaries, including Britain's Prince Charles and the Duchess of Cornwall, Prince Felipe and Princess Letizia of Spain and Denmark's Crown Prince Frederik and his wife.

BBC: Dutch Queen Beatrix abdicates in favour of son