The Sun says that the character, played by Leigh Francis, will answer viewers' questions about embarrassing problems and sexual issues.
"It sounds crazy but we think it will work," a source said. "Through humour, Keith can help people smile again. We'll deal with issues but also make the public laugh along - without laughing at the people with problems. It's a great idea and we hope it will be popular with viewers."
Francis already performs as Keith Lemon alongside This Morning host Holly Willoughby on the ITV2 series Celebrity Juice.
The insider explained: "Leigh and Holly are great mates, but he won't be nicknaming her 'Holly Willoughbooby' on This Morning, that's for sure."
This Morning's current agony aunt Denise Robertson is expected to remain on the programme to deal with the more sensitive issues. Keith Lemon will make his debut on October 7.