Music mogul Simon Cowell has broken his own promise by belting out a tune on X Factor USA.

He swore we would never hear him sing, but 53-year-old Simon Cowell was persuaded by fellow X Factor USA judge Kelly Rowland to show off his vocal talents on the show, which can been seen on the first episode of the show this Thursday.

The singing incident occurred when Simon gave some rather scathing feedback to a contestant after their rendition of the classic Fools Rush In.

First to give their verdict was Demi Lovato who told the hopeful from Denver: ''You would sound like what Simon sounds like when he sings.''

Kelly then urged the soon-to-be-dad, who branded it the ''worst'' day of try-outs ever, to sing the same song.

Surprising everyone on the show, Simon obliged and was even praised by fellow judges Paulina Rubio and Demi, who said his rendition was ''charming''.

Kelly added: ''I knew that voice was always there.''

You can be the judge and decide if Simon really can sing when the episode airs on TV3, Thursday Sept 12 at 9pm.