In accordance with Article 87 of the Constitution, the King cannot simultaneously be the head of state of another country without the consent of both Chambers of the Federal Parliament. A personal union is only possible with the approval of two-thirds of the votes cast in both Chambers, and a quorum of two-thirds of the members of the Chamber must be present in order for the approval to be valid. This article was used only once, in 1885, when King Leopold II of Belgium also became the sovereign ruler of the Congo Free State.