You will need to speak to Drustan, an NPC you can find in Fitzroy’s Gorge inside the cave near the scaffolding.
You can find him again by a balcony in the Alehouse Vestige as you hit the mid point of the burning areas of Calrath city.
The final location is inside the Fief, where you can find a small cottage, with Drustan by an unlit fire freezing to death.

Once you have visited all three of these locations in order, you will now be able to complete Drustan’s questline as part of the Radiance ending. You will find an Umbral Scouring location in a small ruined circular building, where Drustan dies to a moth creature. His gear and brother’s ring will be in an item pickup by an entrance to the ruined building. From there,m as part of the Radiance ending at the end of the Sundered Monarch fight, you will fight another memory of Melchior, with it implying its his body being used as the vessel that brought Adyr’s influence to Bramis Castle.

You can read more on Drustan’s quest here.