In February the club announced that Mills, who was sent packing by the broadcaster two weeks ago following a probe into his personal conduct, was to support the Irish act over two nights.
Shane Lynch's daughter, Billie Rae, has complained about working a minimum-wage job while her famous father sells out stadiums on his band's farewell tour.
The Irish music manager, who worked with Boyzone and Westlife , was a judge on the ITV talent show from its inception in 2004 alongside Simone and Sharon.
Boyzone is set to reunite for two shows at London's Emirates stadium in June - which will be the first time the band has performed together since their London Palladium run in 2019.
The Irish boyband, made up of Ronan Keating, Keith Duffy, Mikey Graham, Shane Lynch and the late Stephen Gately, first shot to fame in the early nighties.