Cowell hit headlines around the world in July (13) when it emerged the eligible bachelor has fathered a child with socialite Lauren Silverman.
The tot is due early next year (14) and Cowell is reportedly determined to avoid both the birth and getting stuck in to diaper duties when the baby arrives, but Walliams is adamant The X Factor boss is simply teasing his critics.
The Little Britain star, who is father to a four-month-old son called Alfred, tells U.K. Tv show host Lorraine Kelly, "I think the thing about the nappies is that it's one of those things that so many men say - 'I'm never going to change a nappy'. It's actually not that bad. It's part of loving your child. It's really, really important... But I think, you know, he has that kind of persona doesn't he, where he kind of likes to wind us all up."