Jogchum Vrielink, professor discrimination legislation at the Saint-Louis University, confirmed it wouldn’t be a problem here either.
Under the Salic Law women were excluded from becoming head of state in Belgium until the law was changed in 1991. Crown princess Elisabeth is set to become the first female Belgian head of state. Vrielink says that as the law says nothing about the gender of the monarch’s partner, it’s quite possible the head of state marries a person of the same sex as Belgium enjoys equal marriage.
Belgium would then have two queens, or possibly three or four, as Queen Mathilde and Queen Paola also bear the title.
Princess Amalia won’t however be able to wed princess Elisabeth as members of the Dutch royal house of Orange-Nassau are excluded from all power and authority in Belgium. It’s in the constitution and a consequence of the unhappy end to the Kingdom of the Netherlands in Belgium in 1830.
On the other hand, Dutch media have been speculating about a relationship between Princess Amalia and Princess Elisabeth’s brother, Prince Gabriël, for some time now. If they wanted to marry, possibly, that could be a constitutional problem.