Internally, the Duke did not want to believe it at first. He wanted to deny it. So, he thought that maybe, Dimo could have misheard.
But the evidence Alwin gathered proved it. There was a record of the Head Butler and Sonia talking about it.
Arabella could vividly recall that he was ashen as he listened, and he looked like he would burst into tears.
The Duke loved Brent and Monica as his own. And he was even willing to continue raising them if only Dimo hadn't heard everything from Sonia and the Head Butler.
Duke Olivier loved Sonia too which was why he was utterly disappointed, hurt, and furious that the latter had only been fooling him from the start.
It was probably one of the reasons why he could not execute Sonia. He still had lingering feelings for her but no longer wanted to be with her after what she had done.