It is one of several books on the relationship between Prince William and fiancee Kate Middleton set to be released ahead of the April 29 wedding at Westminster Abbey.
The book will be published in the U.S. on Dec. 17. It charts the romance between "the boy who would one day be king" and "the middle-class girl who had harbored a crush on him since her school days."
Clench had written most of the text in advance and turned out the final 4,000 words in 48 hours.
Meanwhile, there's a great deal of anticipation as to what the grand wedding will be like.
"Basically the circus is back in town. It's an absolute frenzy. There's so much news, there's so much reporting going on about Kate and William. Everything you would need to know we're being told and a lot we don't need to know. The problem we're facing now is the queen is worried about the paparazzi. She doesn't want Kate to suffer the way Diana did to some extent," said royal biographer Mark Saunders.
Also, there are reports that the major British broadcasters are discussing the possibility of broadcasting the royal wedding in 3D.
The Associated Press contributed to this story.