The principle of loyalty and sincere cooperation is a fundamental principle in the European legal system. Article 4(3) TEU does not only display its significance when it comes to the duty of Member States to ensure, within their domestic legal systems, complete fulfillment of the obligations arising out of the Treaties or resulting from the acts of the institutions of the Union. Article 4(3) TEU also addresses the Union itself which shall, in full mutual respect, assist the Mem