He was not because he missed or felt guilt about supporting Keira's execution when he knew she was his daughter.
BUT... because after she was executed and disgraced this angered the spirits since Keira was indeed the destined Saintess. Who brought havoc onto the world.
In addition his "daughter" whom he publicy declared as the "real" Parvis daughter turned out to a demon possessing dead body of his 1st wife's dead daughter (Keira's mother family were responsible for the death of original Cosette) showed her true colors. Unleashing a demon army to conquer the human realm.
Needless to say when this occured, the masses put the blame squarely on the Duke for what happened. That is why he "reversed" time to save himself and Parvis household's integrity.
People like to say he hands were tied. Yeah right...
There was a vote that decided if to execute Keira or not. He chose to (stepping outside the "neutral" zone) VOTE FOR EXECUTION. And publicly defame her as a "fake" while holding arm with his "real" daughter Cosette.
All while he KNEW KEIRA WAS HIS BIOLOGICAL DAUGHTER!!!!
why am i getting the feeling he was involved with kiera's time travel
like the third person to help with changing of time, and he chose to leave the past memories with kiera