In 2377, he was the Cardassian ambassador to the Klingon homeworld of Qo'noS and was instructed by his superior Supreme Legate Skrain Dukat to request that Regent Martok turn over the Romulan cloaking device which Captain Kurn had captured from the Terran Rebellion at Empok Nor two years earlier for study. Darhe'el reminded the Regent that the Articles of the Alliance specifically stated that any technology seized from a third party by either of their races was to be made freely available to the other for study.
Although Martok had been prepared to eventually turn over the cloaking device to the Cardassians, his Vulcan slave Taurik used his telepathic powers to exacerbate the Regent's distrust towards the Cardassian Union. This resulted in Martok threatening to slice Darhe'el open with his d'k tahg and refusing to supply the cloaking device unless and until the Cardassians provided him with something of equal value. Being no match for Martok in either physical prowess or fighting ability, the terrified Darhe'el almost immediately scurried out of the Great Hall. He reported Martok's refusal to cooperate to Legate Dukat, who was furious. This led to a significant deterioration in Klingon-Cardassian relations. (ST - Mirror Universe novel: Rise Like Lions)