Just a slight clarification, King Charles has properties in the villages of Viscri and Zalanpatak, which are both located in the region of Transylvania not Wallachia. Wallachia is bordered by Transylvania to the north and the Danube River to the south. Wallachia was one of the two original regions that formed modern day Romania. King Carol I was the first monarch of modern day Romania. Transylvania joined Romania after WWI having previously been part of the Austrian Hungarian Empire. King Ferdinand was the monarch when Transylvania united with Romania. My grandparents and my father were all born in Transylvania. However my grandparents were born while it was part of Austrian Hungarian Empire and died after unification. My father was born in Transylvania under King Ferdinand. Much more information than you wanted.

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That might explain the interest Charles, as PoW, had about Wallachia.
IIRC he even bought a home there, at that time.