Max hit on a group geared (TBM/TDS) tank with only 12k AC and 166k HP buffed was about 13,8k. Most annoying is his complete heal. If you are a group only group geared and with not very decent DPS then his Heraldic Assault will be quite a challenge, so remove it fast.
Spells:
Heraldic Assault - Duration: 1.0 min - Range: 200 - AERange: 100 - Resist Disease Adjustment -950 - Decrease ATK by 1352 to 100550 - Decrease Mana Regen by 4417 to 144700 - Decrease Endurance by 4189 to 121900 per tick
Complete Heal - he did this time a complete heal for 3-4 times - it seems it is somehow related to his spell Heraldic Assault, but that is not confirmed.
Radiant Cure removed the Debuff easily. It is highly recommended to remove the debuff if in case it is related to the complete heal cycle you don't have to deal with a longer fight. Group was at about 40% with mana/endurance after the fight and full burn.