Many people have raised doubts on the alleged Christian faith of Republican presidential front-runner Donald Trump, including Pope Francis, but the business magnate has always maintained his Presbyterian Christian upbringing.

Last summer, Trump talked to pollster Frank Luntz at The Family Leader's Family Leadership Summit in Iowa and recalled attending church services during his youth, according to Charisma News.

Trump said he can still clearly remember the sermons delivered by famed evangelist Norman Vincent Peale, who wrote the book "The Power of Positive Thinking" back in 1952.

Although Peale's ideas have not been supported by mind experts and criticised heavily by psychologists, many people have attested that they subscribe to his beliefs.

Peale was even awarded the Presidential Medal of Freedom by former President Ronald Reagan.

When he passed away on Dec. 24, 1993, U.S. President Bill Clinton fondly remembered him: "The name of Dr. Norman Vincent Peale will forever be associated with the wondrously American values of optimism and service. Dr. Peale was an optimist who believed that, whatever the antagonisms and complexities of modern life brought us, anyone could prevail by approaching life with a simple sense of faith. And he served us by instilling that optimism in every Christian and every other person who came in contact with his writings or his hopeful soul."

As for Trump, he also has nothing but nice things to say for his former pastor. "You could listen to him all day long," he said. "And when you left the church, you were disappointed it was over. He was the greatest guy."

Trump credits Peale's teachings—either through his radio shows, newspaper columns, and articles—for having greatly boosted in his self-confidence and Christian faith.