 When Mercedes and Jacqui refuse to be donors, Kathleen tells Billy that he is the father of her daughter Theresa McQueen (Jorgie Porter), confirming that Theresa is actually Mercedes and Jacqui's half-sister.Billy is later revealed to not be needing a kidney, and that it is actually Mercedes, Jacqui and Theresa's secret half-sister, Emily Alexander (Elizabeth Henstridge).However, Mercedes is not interested in Billy nor Emily and declines to be a donor, although Jacqui later agrees to be a donor but is revealed not to be a match, so Billy and Emily disown her and leave.