In the 12th and 13th centuries, during the early Anglo-Norman period, records of a political nature relating to the Déisi and the descendants of the Uí Faeláin dynastic group decline.
Robert Fitz Stephen and Richard, son of Gilbert, i.e. Earl Strongbow, came from England into Ireland with a numerous force, and many knights and archers, in the army of Mac Murchadha [Dermot MacMurrough], to contest Leinster for him, and to disturb the Irish of Ireland in general; and Mac Murchadha gave his daughter to the Earl Strongbow for coming into his army.
They took Loch Garman [Wexford town; a stone walled Norse settlement], and entered Port-Lairge [Waterford town; a Norse settlement] by force; and they took Gillemaire, the officer of the fortress, and Ua Faelain, lord of the Deisi, and his son, and they killed seven hundred persons there.By the beginning of the thirteenth century, most of the territory of the Déisi was absorbed into the Anglo-Norman colony.
The earliest anglicised forms of the Ó Faoláin name were Felan, Faelan, Hyland, with many other similar variants, including Whelan and Phelan in counties Waterford and Kilkenny.
Whelan and Whalen are the most prevalent forms in modern times, and combined are placed seventy-ninth in the list of the hundred most common surnames in Ireland.