Kafin ya yi gwaji don'' The X Factor ', Callahan ya kasance wani ɓangare na rukuni na jinsi da aka gudanar da Geri Halliwell, kafin ya bar shi a watan Yunin 2011 don ya tafi solo.
Tabbas, sigar da ta fi rikitarwa ta jumla ita ce "Kafin ya yi gwaji don 'The X Factor', Callahan ya kasance wani ɓangare na ƙungiyoyi daban-daban har sai ya yanke shawarar yin solo a cikin 2012, yana sakin waƙar farko 'Runaway Train' a watan Disamba na 2012. "