Judgment of the Court (Third Chamber) of 20 May 2021.#Renesola UK Ltd v The Commissioners for Her Majesty's Revenue and Customs.#Reference for a preliminary ruling – Customs union – Assessment of validity – Implementing Regulation (EU) No 1357/2013 – Determination of the country of origin of solar modules assembled in a third country from solar cells manufactured in another third country – Regulation (EEC) No 2913/92 – Community Customs Code – Article 24 – Origin of goods whose production involved more than one third country – Concept of ‘last substantial processing or working’.#Case C-209/20.