Blizzard and Random House Worlds just announced an official prequel novel to the upcoming Diablo 4 expansion, Lord of Hatred. Diablo 4: The Lost Horadrim sets the stage for Lord of Hatred that is billed as a companion novel and "an essential chapter" for the expansion.
Diablo 4: The Lost Horadrim will go on sale on April 21, 2026. The physical hardcover release will run you $30. There also appears to be a Kindle and eBook...