Rumour has it the reason we didn't see the behemoth come to fruition is because it actually IS the Duke.
The lore says that The Duke, just like a literal Big Brother*, was actually a sibling. He had long since turned thanks to an accident with a virus he was going to weaponize.
(*Reference to Orwell's 1984??)
He had only one other sibling that we are made aware of, a younger sister, since the 2nd child; a middle brother, was killed in a failed ambush of the White River Settlers who were relocating to the deep south from northern Navezgane.
The sister was to be the successor of the empire by order of The Duke '...in the event of...' what is only described as '...unfortunate circumstances.'
Post-exposure to the virus, The Duke requested to be shot if* and when he turned, being a man of honour and pride he couldnt face the shame of suicide. The younger sister however saw the suffering in The Duke's eyes as he threw himself around in pain during his pre-turn death throws. Unable to take such misery, she selfishly betrayed her brothers wishes and instead had him sedated.
(*Details of the accident are not given, and it is unclear how or to what extent The Duke came into contact with the virus.)
When he was unconscious she ordered the generals who sat at The Dukes side all through the events to have him bound in chains.
(What happened next, I think, leads to a conflict between the lore and the actual game.)
The Dukes sister had him bound with his feet set in concrete, rooted, in reinforced steel sarcophagus with a single small glass panel so she could look upon her brother.
For the love and respect of The Duke, and his wishes*, she couldnt kill him, and neither would she allow anyone else.
(*Though it is questionable that she actually respected his wishes since she betrayed his final request.)
Bad news comes, as I read, when The Dukes sister is out of the casino to address a potential alliance with a small north eastern faction who also recently lost their leader, though alliance for the younger sister likely means absorbption.
While away, an act of sabotage had taken place as one of the high ranking members (referred to as '...a subordinate to [his] Generals) unwittingly ended up giving his own life to break open the sarcophagus and damage the chains.
Thinking he had gotten away with it, he paid dearly. The Duke having turned, burst out of his binding and tore the man to pieces.
There is no mention of which faction, if any, this traitor/spy/defector belonged to. Some say he was White River, some say he was an Ash Jackal (??) But it's all speculation unless we are given details on the lore.
This retelling ended with only one thing. Upon hearing of the incident and returning to the casino, The Dukes sister found the basement half destroyed.
The Dukes corrupted flesh could still be seen in the holding block as two disembodied feet - so seeming whatever he had become had torn itself out of its own extremeties to be free.
Blood trailed from the holding room up the corridor leading to the main underground staircase, the trail running thin before eventually stopping.*
(*This leads me to think perhaps the regenerating zombies may have had the ability in this case to restore lost limbs? Genetically modified by one of The Dukes ex Higashi staff?)
This ends with the sister finding no body, only the side doors leading to a deck on the west wing of the upper second floor of the casino thrown open.
The only mention of The Dukes members and workers was that of those 14 footmen, 2 cooks and one runner, who were '... in a state of perpetual tremor, struck dumb, their faces hung as images of pure horror.'
They are reported as being unable to speak of what they had seen, or anything else.
Whether the young sister found her brother and administered a cure noone knows...
We will know if and when he appears, I suppose.
Any suggestions why the weaponized virus would enable regeneration? It seems conflicting to have your enemies able to reverse battle damage.
What do you guys think? Maybe The Duke changed his mind on what to do with the virus..