On those grounds, the Court (Grand Chamber) hereby rules: 1. 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. 2. 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. That requirement of compatibility with the principle of proportionality is not satisfied where such a decision is based on administrative traffic offences which, under the applicable provisions of national law, give rise to a mere pecuniary penalty. [Signatures] * Language of the case: German.