as Lord Lieutenant over Ireland by Queen Elizabeth I. Some of these letters were written in cipher, but the key to the cipher was to use a substitute letter six spaces earlier in the alphabet. In the letter from Carew to Mountjoy dated 28 May 1602, Carew reported to Mountjoy "One James Blake...took a solemn oath to do service...and is gone into Spain with a determination (bound with many oaths) to kill O'Donnell", and then another letter, written partially in cipher, was sent from Carew to Mountjoy dated 9 October 1602, "O'Donnell is dead... he is poisoned by James Blake, of whom your lordship hath been formerly acquainted...". With his death Spanish plans to send further assistance to the Irish clans were abandoned. It is, however, unlikely that he was poisoned. A more probable cause of death was the tapeworm that Simancas documents of the time stated to be the cause of his demise. It should be said that spies often make improbable claims for their actions, and in this case, as in many others, it seems very likely that Carrew exaggerated the success of his actions. O'Donnell's Last Will and Testament, written in his dying moments with his loyal retinue, is an extremely evocative and moving document. One original is preserved in Simancas and the other in the Chancellery archive in Valladolid. He was buried in the chapter of the Franciscan monastery in Valladolid. Though the building was demolished in 1837, the exact location of the tomb may have been discovered following a Spanish archaeological dig in May 2020. If his remains are successfully identified, they will be returned for burial in County Donegal. Thomas McGreevy's poem Aodh Ruadh Ó Domhnaill describes a search for his grave:Juan de Juni, the priest said,Each J becoming H,Berruguete, he said,and the G was aspirate,Ximénez, he said thenAnd aspirated first and last.But he never saidAnd -- it seemed odd -- heNever had heardThe aspirated nameOf the centuries-deadBright-haired young manWhose grave I sought.McGreevy describes how, whenThey broughtHis blackening bodyHereTo restPrinces cameWalkingBehind itAnd all Valladolid knew And out to Simancas all knew Where they buried Red Hugh.Aodh was succeeded as chief of the Clan O'Donnell by his brother, Rory O'Donnell, created the 1st Earl of Tyrconnell the following year by the English Crown. Rory succeeded Red Hugh as both King of Tír Chonaill and leader of the Red Hugh O'Donnell faction within the divided dynasty.