Diablo 4's ending left fans wanting for more, and we're talking about this in a narrative sense. After beating Lilith to end her bid to wage war on both Heaven and Hell, players are treated to a cliffhanger ending. Mephisto, the Lord of Hatred and one of the three Prime Evils as well as the father of Lilith, is implied to have corrupted Nyrelle to board a ship to go somewhere far away, presumably to find a way to free himself and, possibly, his two brothers, Diablo and Baal, from the Soulstone. We haven't really heard much from Blizzard since then. Instead, the development team has hunkered down and focused on improving the gameplay first. Now that Diablo 4 is in a much better place, it appears Blizzard is preparing for the first of many expansions coming to Diablo 4.
As fans eagerly anticipate the continuation of the, it seems the game's first major expansion might center around one of the three Prime Evils.
This rumor comes from a datamined technical alpha build of Diablo 4 version 2.0, said to be an early build of the game that Blizzard is testing ahead of its release at some point next year.
As previously mentioned, Lord of Hatred is the epithet of Mephisto. In addition to his involvement in the events of the game, both directly and indirectly, the oldest of the Prime Evils appeared in a "secret" post-credits ending as well. When you consider how he pretty much orchestrated the downfall of his own daughter, it's clear Mephisto, with help from an unknown few, will serve as the primary antagonist of this DLC.
