48Thus, a derived right of residence of a third-country national who is a family member of a Union citizen exists, in principle, only when it is necessary in order to ensure that the Union citizen can exercise his freedom of movement effectively. The purpose and justification of a derived right of residence are therefore based on the fact that a refusal to allow such a right would be such as to interfere, in particular, with that freedom and with the exercise and the effectiveness of the rights which Article 21(1) TFEU affords the Union citizen concerned (see, to that effect, judgments of 8 November 2012, Iida, C‑40/11, EU:C:2012:691, paragraph 68; of 12 March 2014, O. and B., C‑456/12, EU:C:2014:135, paragraph 45; and of 13 September 2016, Rendón Marín, C‑165/14, EU:C:2016:675, paragraphs 36 and 73).
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