This is the 2017 facsimile edition of Realm of Chaos: Slaves to Darkness. This edition is being sold as an exclusive item at Warhammer World in Nottingham, England (list price 36£) and is only available to be purchased in person there or at certain convention appearances.
From a sticker applied to the shrinkwrap covering the facsimile edition:
"Realm of Chaos: Slaves to Darkness was the first of two books to explore the insidious nature of Chaos in the Warhammer, Warhammer 40,000 and Warhammer Fantasy Roleplay game systems. Originally published in 1988, its ornately illustrated pages intorduced comprehensive rules and background for the legions of Daemons and mortal servants aligned to the dark gods Khorne and Slaanesh. Also within can be found the first detailed descriptions of the hideous effects of Chaos sorcery, as well as arcane knowledge regarding the link between psykers and the Immaterium.
Produced to celebrate the 30th Anniversary of the release of Realm of Chaos: Slaves to Darkness, this special edition facisimile recreates in stunning detail this iconic piece of tabletop wargames history. Whether you are new to the hobby or have been with us from the start, we hope you enjoy this book."
The facsimile edition appears to be identical to the Second Printing, with the addition of "Copyright 1988, 1991 and 2017 Games Workshop Ltd." on the back cover.