New book sheds light on turmoil of Prince Charles and Princess Diana's marriage

— -- A new tell-all book about the life of Prince Charles reveals details about his marriage to Princess Diana that had been largely unknown to the public.

Charles, 68, and Diana, who died in 1997 in a Paris car crash, almost didn’t make it to their July 1981 wedding, according to the book “Prince Charles: The Passions and Paradoxes of an Improbable Life,” by royal biographer Sally Bedell Smith.

“This book really explores the fact that they were deeply unhappy, or at least Diana was, from literally Day One of their marriage,” Royah Nikkhah, the royal correspondent for The Sunday Times, told ABC News.

Charles got cold feet before proposing to Diana, who was then 19, Smith writes. A letter from his father, Prince Philip, urged Charles, then 32, to make up his mind.

“Prince Philip wanted to be fair to Diana because he didn’t want her reputation as this young 19-year-old in British society ruined,” Nikkhah said. “He spelled this out to Charles in a letter, saying, ‘Look, you know, the time has come. You need to either marry her or cut her loose.’”

Charles experienced cold feet again before marrying Diana, according to the book.

“Going into something like this, I think, he felt that was it for life, and as he wasn’t sure of the relationship, and I think he felt incredibly trapped, probably, on the eve of his wedding,” Nikkhah said.

Despite constant fights with Diana, Charles was by all accounts a loving and devoted father to their sons, Prince William and Prince Harry. The portrayal of Charles in the book is very different from the sometimes stern and removed public image Charles projects.

Charles, the future king of England, was said to return from royal engagements as often as possible to give his sons baths and put them to bed.

He went on to marry Camilla Parker Bowles in 2005. The two, who will meet with Pope Francis on Tuesday in Italy, had a longtime friendship and rumored relationship before their marriage.

Parker Bowles, 69, now the Duchess of Cornwall, divorced her first husband, Andrew Parker Bowles, in 1995. Charles and Diana divorced the next year.

“The key thing with this book, it just heightens the fact that for Charles, there was never anybody else. There was never anyone else who was going to fit all his needs,” Nikkhah said. “It was always Camilla.”

“Prince Charles: The Passions and Paradoxes of an Improbable Life” goes on sale Tuesday.