As Peggy McCracken remarks in The Romance of Adultery, medieval romances’ preoccupation with adulterous queens indicates the high premium placed on legitimate succession in royal lineage and the perceived threat of feminine sexual transgression undermining masculine power. Although courtly love is not the primary focus of the fourteenth-century Of Arthour and of Merlin, its treatment of Arthur’s mother Ygerne in translating the Vulgate Lestoire Merlin suggests that, despite her unimpeachable loyalty, she is somehow an unsuitable mother for Arthur. In her associations with France, her series of husbands prior to Uther and, most significantly, in her sexual attractiveness, Ygerne is depicted as a faithful wife who commands great personal loyalty but who is inextricably connected with the foreign and sensual. Merlin therefore takes care to separate Arthur from her specifically: though her name and motherhood are used to muster supporters for Arthur, she cannot be permitted to nurse him or (unlike Uter) see him after he is taken by Merlin to be fostered by Antor. Through an examination of historical treatment of medieval queens as mothers and a comparison with other queens and mothers in Of Arthour and of Merlin, I argue that her motherhood functions simultaneously a source of political power to him and a vector of adulterous courtly love that must be exorcised to maintain the country’s political and ethnic unity–not because of anything she has done, but because of what she represents in a text highly concerned with the disruptive possibilities of kings and queens marrying for love.