Besides three residences for the monarch the Belgian state also provides the homes for King Albert II and Queen Paola (the Belvedere), Stuyvenberg castle was the residence provided by the state for Queen Fabiola. On the grounds of that residence a large new villa was constructed for Princess Astrid and her family and prince Laurent lives at villa Clementine.
Only the Royal Palace in Brussels and Laeken Castle are directly owned by the Belgian state and get financed with tax money. All the other residences are part of the Royal Trust which is an autonomous institution and financially completely independent and self-sufficient.
I guess it’s safe to assume that the future residence of Princess Elisabeth (Belvedere castle comes to mind) will be a property owned and managed by the Royal Trust.
https://www.monarchie.be/en/royal-initiatives/royal-trust
https://en.wikipedia.org/wiki/Royal_Trust_(Belgium)
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