entitlement to those rights but also the very status of citizen of the Union, even though they have sought, by becoming naturalised in the host Member State, to become more deeply integrated in the society of that Member State, falls within the scope of the Treaty provisions relating to citizenship of the Union. 44 In view of the above, the answer to the first question is that the situation of a person who, having the nationality of one Member State only, renounces that nationality and loses, as a result, his or her status of citizen of the Union, with a view to obtaining the nationality of another Member State, following the assurance given by the authorities of the latter Member State that he or she will be granted that nationality, falls, by reason of its nature and its consequences, within the scope of EU law where that assurance is revoked with the effect of preventing that person from recovering the status of citizen of the Union. The second question 45 By its second question, the referring court asks, in essence, whether Article 20 TFEU must be interpreted as meaning that the competent national authorities and, as the case may be, the national courts of the host Member State are required to ascertain whether the decision to revoke the assurance as to the grant of the nationality of that Member State, which makes the loss of the status of citizen of the Union permanent for the person concerned, is compatible with the principle of proportionality in the light of the consequences it entails for that person’s situation. 46 As noted in paragraph 38 above, the status of citizen of the Union conferred by Article 20(1) TFEU on every person holding the nationality of a Member State is destined to be the fundamental status of nationals of the Member States. In that regard, Article 20(2)(a) TFEU provides that citizens of the Union are to enjoy the rights and be subject to the duties imposed by the Treaties and have, inter alia, the right to move and reside freely within the territory of the Member States. 47 Where, in the context of a naturalisation procedure initiated in a Member State, that State, by virtue of the powers it has to lay down the conditions for acquisition and loss of nationality, requires a citizen of the Union to renounce the nationality of his or her Member State of origin, the exercise and effectiveness of the rights which that citizen of the Union derives from Article 20 TFEU require that that person should not at any time be liable to lose the fundamental status of citizen of the Union by the mere fact of the implementation of that procedure. 48 Any loss, even temporary, of that status means that the person concerned is deprived, for an indefinite period, of the opportunity to enjoy all the rights conferred by that status. 49 In that respect, it must be borne in mind that the principles stemming from EU law with regard to the powers of the Member States in the sphere of nationality, and also their duty to exercise those powers having due regard to EU law, apply both to the host Member State and to the Member State of the original nationality (see, to that effect, judgment of 2 March 2010, Rottmann, C‑135/08, EU:C:2010:104, paragraph 62). 50 It follows that, where a national of a Member State applies to relinquish his or her nationality in order to be able to obtain the nationality of another Member State and thus continue to enjoy the status of citizen of the Union, the Member State of origin should not adopt, on the basis of an assurance given by that other Member State that the person concerned will be granted the nationality of that State, a final decision concerning the deprivation of nationality without ensuring that that decision enters into force only once the new nationality has actually been acquired. 51 That said, in a situation where the status of citizen of the Union has already been temporarily lost because, in the context of a naturalisation procedure, the Member State of origin withdraws the nationality of the person concerned before that person has actually acquired the nationality of the host Member State, the obligation to ensure the effectiveness of Article 20 TFEU falls primarily on the latter Member State. That obligation arises, in particular, where that Member State decides to revoke the assurance previously given to that person as to the grant of nationality, since that decision may have the effect of making the loss of the status of citizen of the Union permanent. Such a decision can therefore be made only on legitimate grounds and subject to the principle of proportionality.