The debate on the fragmentation of International Law has been relatively dormant in recent years. However, recent events demonstrate not only that this debate should be re-awoken, but also that some key elements in this debate must be reconsidered. Notably, while the fragmentation of International Law has often been discussed from the perspective of courts and judges, this paper examines the view and the impact of a different institutional actor – the Commission of the European Union. This paper analyses a series of amicus briefs that were submitted in a number of investment treaties-based cases. These briefs, which were recently disclosed to the author, reflect a certain ‘radicalisation’ of the European Court of Justice’s view concerning the place and the role of the EU legal system within the international legal order. This paper discusses the problematic implications that the Commission’s approach may have on the international legal order, as well as possible future pathways.