But O'Donnell died at Simancus, being assisted on his death-bed by Ó Maolconaire (Four Masters, ad an. 1602) who also accompanied the remains to their last resting place in the Franciscan church at Valladolid.
Ó Duinnshléibhe was one of two Donegal men named Father Muiris Ulltach who attended Aodh Ruadh Ó Domhnaill (d. 1602) on his death-bed in Simancas Castle, Spain, with Archbishop of Tuam Fláithrí Ó Maol Chonaire.