This case commentary analyzes the ruling of the Paris Court of Appeal of December 5, 2023 in relation to the petition to set aside an arbitration award based on the arbitrator’s failure to disclose certain facts. The court found, in line with French jurisprudence on the duty to investigate and waiver (Art. 1466 Civil Procedure Code),that the notorious facts, in existence after the initiation of the proceeding, were not likely to create reasonable doubts about the impartiality of the arbitrator. The decision acts as a double-edged sword: it expands the exemption to disclose notorious facts on one side, and the duty to investigate and waiver on the other. Perhaps in a newfound equilibrium between arbitrator and parties’ duties, the ESISCO case aligns with comparative nascent case-law in common law jurisdictions on the duty to reasonably investigate, and the brand new “duty to reasonably enquire” of the 2024 IBA Guidelines on Conflicts of Interest (standard 4(a)).