Simon Cowell, the British reality television mogul, said last night that he would resign as a judge of American Idol in May, severing his ties with a blockbuster media franchise that has dominated ratings and earned more than $8 billion (£5 billion) over its eight-year run.

“What we have agreed is that The X Factor will launch in America in 2011 with me judging the show and executive producing. Because of that, this will be my last season on American Idol this year.”

Madonna has been mooted as one possible replacement.