Prince Harry's memoir is the U.K.'s fastest selling non-fiction book

Prince Harry's new memoir, "Spare," became the fastest selling non-fiction book in United Kingdom history on its first day on sale, Reuters reports.

Driving the news: "We always knew this book would fly but it is exceeding even our most bullish expectations," said Larry Finlay, Transworld Penguin Random House's managing director, in a statement, per Reuters.

• Since it came out, 400,000 copies of the book have been sold in hardback, e-book and audio formats, per Reuters.
• "As far as we know, the only books to have sold more in their first day are those starring the other Harry [Potter]," Finlay said.

Zoom out: The memoir is part of a new media empire that Harry and his wife, Meghan Markle, are building around their lives, Axios' Hope King reports.

• Excerpts of the book were mistakenly released early and contained details on private conversations among the Royal Family, AP reports.

Go deeper... Harry and Meghan speak out on royal family's "unconscious bias" in Netflix series