The hotly anticipated book from South Korean boy band BTS was released Sunday and wasted no time hitting the top of the charts, according to the Hollywood Reporter.

Flatiron published Beyond the Story: 10-Year Record of BTS, written by the band and Myeongseok Kang, reportedly containing “stories that go beyond what you already know about BTS, including unreleased photos, QR codes of videos, and all album information.”

As of Monday afternoon, the memoir was the No. 1 bestselling book on the websites of both Amazon and Barnes & Noble. The success of the book was predictable—the phenomenally popular band has a dedicated following called ARMY, and Flatiron timed the release of the book to happen on ARMY Day, dedicated to BTS’ fans.

The book caused waves before anyone actually knew what it was. In May, rumors circulated on TikTok that a mystery book from Flatiron would be a memoir by musician Taylor Swift. Days later, the publisher confirmed that the book would actually be by BTS.

The Associated Press ran a review of the book on Monday, calling it “a love letter to the community that made their career and a reminder that there is always more to learn about them.”

“At each turn, the band speaks from a personal perspective, outlining their hopes, thoughts, feelings, and experiences—the unrivaled access that sets this official biography apart from the countless unofficial others,” critic Maria Sherman writes. “Many of these stories will be familiar to ARMY, but the band’s personal recollections [provide] a feeling of freshness.”

Michael Schaub, a journalist and regular contributor to NPR, lives near Austin, Texas.