The 93-year-old monarch's dresser Angela Kelly - who has worked with the royal since 1994 - will discuss her 25 years as Personal Advisor and Curator (The Queen's Jewellery, Insignias and Wardrobe) and In-house Designer after being given "extraordinary permission" to speak about her "working relationship" in 'The Other Side of the Coin: The Queen, the Dresser and the Wardrobe.
The book will include unseen photograph's from Angela's personal collection and stories about their bond and how they prepare for formal occasions.
Samantha Cohen CVO, Assistant Private Secretary to The Queen, said: "This book documents the unique working relationship between Her Majesty The Queen and the woman who has been her Personal Advisor and Senior Dresser for more than two decades: Angela Kelly.
"It gives a rare glimpse into the demands of the job of supporting the monarch, and we gain a privileged insight into a successful working relationship."
This is the first time a working member of the royal household has been given permission to speak so candidly about their position.
A spokesperson for HarperCollins said: "The Queen has personally given Angela her blessing to share their unparalleled bond with the world.
"Angela Kelly is the first serving member of the Royal Household to have been given this extraordinary permission.
"Whether it's preparing for a formal occasion or brightening Her Majesty's day with a playful joke, Angela's priority is to serve and support.
"Sharing never-before-seen photographs - many from Angela's own private collection - and charming anecdotes of their time spent together, this revealing book provides memorable insights into what it's like to work closely with The Queen, to curate her wardrobe and to discover a true and lasting connection along the way."