European Union – Citizenship of the European Union. Article 21(1) of the Treaty on the Functioning of the European Union should be interpreted as requiring the member state of which a Union citizen was a national to facilitate the provision of a residence authorisation to the unregistered partner, a third-country national with whom that Union citizen had a durable relationship that was duly attested, where the Union citizen, having exercised his right of freedom of movement to work in a second member state, in accordance with the conditions laid down in Directive (EC) 2004/38, returned with his partner to the member state of which he was a national in order to reside there. The Court of Justice so held in a preliminary ruling in proceedings concerning the refusal by the applicant Secretary of State for the Home Department (UK) to issue the respondent, a third-country national, with a residence card after she had moved to the UK with her unmarried partner who was a UK national.