12 J. Shaw host member state will no longer benefit from Directive 2004/38 (and thus no longer has the family reunion rights conferred under the Directive on mobile EU citizens). However, she will benefit still from her status as an EU citizen under Articles 20 and 21 TFEU. This means that the host state must grant her rights to family reunion that are no more restrictive than those laid down in the Directive. What makes this controversial is that the EU citizen in these circumstances benefits from EU law measures on family reunion that are notably less restrictive than the national rules applicable in most member states for citizens.25 The lack of symmetry in the dual nationality rules applied by the member states across the EU means that this approach, while superficially attractive in terms of special protection of the interests of those who go so far as to naturalise in the host state, has an unhelpful aura of arbitrariness about its scope of application. For example, it would seem that if the Lounes case, involving a Spanish woman acquiring UK citizenship and keeping her Spanish citizenship, and benefiting from family reunion with her Algerian partner, were reversed, the position would not be the same. Suppose that a British woman resident in Spain were to acquire Spanish citizenship by naturalisation. The theoretically stricter requirements in relation to dual citizenship in Spain would mean that she would not be able to continue benefiting from her UK citizenship under Articles 20 and 21 TFEU because, at least as far as the Spanish authorities would be concerned, she would have renounced that nationality. Can EU citizenship be retained after Brexit? The developments in relation to the constitutional constraints generated by EU citizenship may prove to be of central importance when it comes to figuring out the effects of Brexit on EU citizenship (and indeed of EU citizenship on Brexit). The orthodox international law-based position would be as follows: once the UK leaves the EU, the Treaties and the various rights and obligations applicable under them no longer apply. Absent a consensual arrangement under Article 50 TEU in the exit negotiations, the treatment of EU27 citizens resident in the UK and UK citizens resident in the EU27 reverts to being a matter for national immigration law subject only to certain international human rights obligations. Each member of these two groups has to seek stable legal residence from their host state. At most, those in this situation could benefit from residual protection of their family life interests 25 See Peers, S. (2017), ‘Dual citizens and EU citizenship: clarification from the ECJ’, EU Law Analysis Blog, 15 November 2017, available at http://eulawanalysis.blogspot.com/2017/11/dual-citizens-and-eu-citizenship.html.