Fourth Wing, the previous installment, follows Violet's journey as she trains to become a dragon rider while navigating personal challenges related to a genetic condition.

In a heartfelt Instagram message, Yarros thanked her fans and encouraged them to enjoy her new book.

Rebecca Yarros's latest release, Onyx Storm, marks the third installment in her Empyrean series and has generated significant excitement among fans, establishing it as a major publishing event for the year.

Published by Little, Brown, Onyx Storm is anticipated to be the publisher's biggest pre-ordered title since the Harry Potter play script launched in 2016.

The new book is described as a crucial turning point for the protagonist, Violet Sorrengail, who must face real battles without the benefit of further training.

In the US, some readers eagerly awaited as late as 3am for an exclusive edition from Target, which experienced website issues due to overwhelming demand.

Rebekah West, editorial director at Little, Brown's Piaktus imprint, remarked that the level of enthusiasm for Onyx Storm is reminiscent of the Harry Potter phenomenon.

Waterstones expects that Onyx Storm will significantly exceed the first-day sales of its predecessor.

Social media is abuzz with readers expressing their excitement, with some even contemplating calling in sick to dive into the book immediately.

Yarros has made a name for herself in the 'romantasy' genre, with her previous works, Fourth Wing and Iron Flame, achieving best-seller status in both the US and the UK.

To celebrate the release, nearly 60 Waterstones branches held special events, including midnight openings on January 20 and early openings on January 21.