In 2009 Lady Gaga was supposed to go on a planned co-headlining concert tour with a famous rapper. The tour was canceled. But who was the rapper?

Explanation

"The Fame Ball Tour" (2009) was the debut concert tour by Lady Gaga, in support of her debut studio album "The Fame". Her second concert tour was "The Monster Ball Tour" (2009-11) and her third was called "Born This Way Ball" (2012-13). The "Born This Way Ball Tour" became one of the highest-grossing tours of all time.