On those grounds, the Court (Second Chamber) hereby rules:
Article 21 TFEU must be interpreted as not precluding the authorities of a Member State, in circumstances such as those in the main proceedings, from refusing to recognise all the elements of the surname of a national of that State, as determined in another Member State – in which that national resides – at the time of his or her adoption as an adult by a national of that other Member State, where that surname includes a title of nobility which is not permitted in the first Member State under its constitutional law, provided that the measures adopted by those authorities in that context are justified on public policy grounds, that is to say, they are necessary for the protection of the interests which they are intended to secure and are proportionate to the legitimate aim pursued.
52) It must be noted as a preliminary point that a person’s name is a constituent element of his identity and of his private life, the protection of which is enshrined in Article 7 of the Charter of Fundamental Rights of the European Union and in Article 8 of the European Convention for the Protection of Human Rights and Fundamental Freedoms. Even though Article 8 of that convention does not refer to it explicitly, a person’s name, as a means of personal identification and a link to a family, none the less concerns his or her private and family life (see, inter alia, European Court of Human Rights judgments Burghartzv.Switzerland of 22 February 1994, Series A No 280-B, p. 28, § 24, and Stjernav. Finland of 25 November 1994, Series A No 299-B, p. 60, § 37).
89) The European Union legal system undeniably seeks to ensure the observance of the principle of equal treatment as a general principle of law. That principle is also enshrined in Article 20 of the Charter of Fundamental Rights. There can therefore be no doubt that the objective of observing the principle of equal treatment is compatible with European Union law.