This note reports an observation of a fatal attack on a female Eastern Koel Eudynamys orientalis by three Little Friarbirds Philemon citreogularis and a Black Butcherbird Cracticus quoyi. The Eastern Koel is a brood-parasite, with the Little Friarbird a known host and the Black Butcherbird a potential host. The attack occurred during the breeding season of all three species. However, upon dissection, the female Koel was found to have an ovary in nonbreeding condition and an empty oviduct, suggesting that extremely aggressive behaviour towards brood-parasitic cuckoos may not be strictly directed at individuals attempting to lay. Although there are some records of fatally aggressive behaviour by potential hosts towards brood-parasitic cuckoos, no fatal attacks on Koels have been reported previously. Although the Black Butcherbird is not a confirmed host for Eastern Koels, its aggressive behaviour suggests that it sees the Koel as a potential threat.