Cowell, 53, is reportedly having a baby with his friend Andrew Silverman's estranged wife Lauren Silverman, reported Contactmusic.
"I've not heard anything officially. But if it's true then I'm absolutely delighted. It's wonderful! He'll make a fantastic father. He'll be great," Julie said.
Rosy Davis, who is married to Silverman's father Steven, confirmed the news and admitted her family are "excited" that she is welcoming a child with the 'X Factor' boss.