Kelly Rowland says Simon Cowell is a ''smart ass''.

While the 32-year-old singer loves working with him on 'X Factor USA', she says she has to work hard to keep him in check.

Kelly - who has just joined the panel of the talent show - said: ''I love Simon! Of course he's a smart ass but he's very insightful. He does get on my nerves sometimes but in a good way. He thinks I'm crazy and I tell him to shut up.

''I want to make sure I'm not a dream crusher on the show. It's about being honest and giving constructive advice.''

Kelly is part of a new look judging panel for this year's series.

She and Paulina Rubio have replaced departing experts Britney Spears and L.A. Reid and make up the panel with Demi Lovato and Simon.

Britney, 31, signed a sensational $15 million deal to appear on the show but left after just one season, while executive L.A. quit his position after two seasons to concentrate on running his Epic Records music label.

Former Destiny's Child star Kelly previously acted as a judge on the UK version of 'The X Factor'.