We've datamined a new legendary weapon with the first PTR build for Season of Discovery Phase 5.
The weapon in question is Hammer of the Lightbringer, Uther's two-handed mace.
The «mace» (currently classified as a sword) has a dungeon tag for the new Burning of Andorhal dungeon. This could mean that it is only usable while inside that dungeon, similar to Kael'thas' weapons in Tempest Keep.
Or it could also mean it is created while inside the new dungeon.
This build also adds more Uther and Silver Hand-themed items like Scrap of Torn Cloth, Blood of the Lightbringer and Ada's Amulet. The mace also has an effect to turn into Truthbearer to be used as a one-hander with a shield, likely meaning it can be used for Tank and Healing Paladins as well.