"In royal circles, it is no secret that he does not share the King's sense of the spiritual, let alone the late Queen's unshakeable devotion to the Anglican church," the expert penned.
"His father is very spiritual and happy to talk about faith but the Prince is not. He doesn't go to church every Sunday, but then nor do the large majority of the country. He might go at Christmas and Easter but that's it," the author then quotes a senior palace figure as saying.
"He very much respects the institutions but he is not instinctively comfortable in a faith environment."
The late Queen Elizabeth was well known for her strong religious convictions, attending church weekly through her record 70-year reign, with insider sources previously reporting that her faith "sustained" her.
"God holds her and her family in his hands. It is the solid and simple faith that sustains the Queen," they shared with PEOPLE in May 2020.
"Her Christian faith means so much to her."
As for Charles, following the death of his mother in September 2022, he automatically became the Supreme Governor of the Church of England, going on to describe his faith as "deeply rooted" in the Anglican church in his inaugural speech as sovereign the following day.
During his coronation ceremony on May 6, 2023, Charles also promised to maintain the Protestant faith and the Church of England.
Whilst he was confirmed into the Anglican faith in 1997, only time will only tell if Prince William decides to do things differently and take a step back from the religious aspects of his future role as King.