Despite taking it all in good humour in public, Britain's Got Talent boss Simon Cowell is said to be "fuming" with David Walliams after making jokes about his sexuality.
In a recent appearance on the Jonathan Ross show, David repeated mocked the music mogul over his love life.
And the Little Britain comic has been making similar jokes on the set of the series, which are beginning to get to Simon.
"Simon took David's baiting on Jonathon Ross show very well in front of the cameras but he was absolutely seething when they came off," a source tells Star magazine this week. "He felt he had been publicly humiliated in front of millions of viewers. He will not stand for that and told David to quit the backchat at his expense."
The insider added: "He simply won't put up with being the butt of David’s jokes. He's brought David to join the panel to increase the show’s popularity, not to have his image tarnished"
However David recently insisted that Simon wasn't taking his teasing too seriously.
“Simon is the best boss you could ever hope for in the world, because he really likes you to take the mickey out of him,” David said.
“I wasn’t sure if he would, I’ve met him a few times over the years before Britain’s Got Talent, but I wouldn’t say I know hm.”
Britain's Got Talent 2012 continues this Saturday night on ITV1.