Halfdan is not described as ruling in Ireland like his brothers in any contemporary source .
Halfdan is instead described as one of the leaders of the Great Heathen Army which invaded the Anglo - Saxon kingdoms of England from 865 onwards .
Halfdan is not described as ruling in Ireland like his brothers in any contemporary source , but he is instead described as one of the leaders of the Great Heathen Army which invaded the Anglo - Saxon kingdoms of England from 865 onwards .