Judgment of the Court (Grand Chamber) of 31 January 2020.#Republic of Slovenia v Republic of Croatia.#Failure of a Member State to fulfil obligations — Article 259 TFEU — Jurisdiction of the Court — Determination of the common border between two Member States — Border dispute between the Republic of Croatia and the Republic of Slovenia — Arbitration agreement — Arbitration proceedings — Notification by the Republic of Croatia of its decision to terminate the agreement because of an irregularity alleged by it to have been committed by a member of the arbitral tribunal — Arbitration award made by the arbitral tribunal — Alleged failure by the Republic of Croatia to observe the arbitration agreement and the border established by the arbitration award — Principle of sincere cooperation — Request that a document be removed from the case file — Protection of legal advice.#Case C-457/18.