The Elder Scrolls Online website has details about Dark Brotherhood, the next expansion for The Elder Scrolls Online: Tamriel Unlimited (thanks Acleacius). This is currently on the test realm for the MMORPG, and it is expected to go live for Windows and OS X on May 31st. This will be accompanied by a patch with changes and the enhancements for the base game. Here are the details:

The Dark Brotherhood is looking for a few good killers. Explore the Gold Coast and discover if you have what it takes to join the ranks of Tamriel's master assassins in the Dark Brotherhood DLC game pack. From the port city of Anvil to the Great Cathedral of Kvatch, the business of the Brotherhood consists of murder and mayhem—and business is good! Join the Brotherhood, enter the Sanctuary, and accept your first contract from the mysterious Speaker. Kill well, assassin!

Dark Brotherhood, the latest DLC game pack for The Elder Scrolls Online: Tamriel Unlimited, will be available on the ESO PTS (Public Test Server) later today and launches on PC/Mac on May 31st, and both Xbox One and PlayStation®4 on June 14th. The Dark Brotherhood DLC game pack—complete with a new Dark Brotherhood passive skill line, an all-new PVE area of Cyrodiil called the Gold Coast, hours of new story content and more—will be accessible at no cost to those who have an active ESO Plus membership. Otherwise, it will cost 2,000 crowns in the ESO Crown Store.

The base-game patch that accompanies Dark Brotherhood, free to anyone who owns ESO, is packed with new features and enhancements including the removal of Veteran Ranks, Poison-Making (an all-new addition to Alchemy), nameplates and console character name display, and tons of combat and gameplay balance changes. We encourage all our PC and Mac players to join us on the PTS later today for Dark Brotherhood testing!