Clara didn't want to have much to do with Zach either after finding out about his true identity but she was reluctant to reveal such information to anyone else.
She wasn't willing to mock Zach like Grace and her servants but she couldn't treat him so perfunctorily either.
Just as Grace was about to laugh in jubilation, a burst of thunder spread across the sky like a web of interconnected blood vessels and shut up everyone else in the surroundings. His earlier words became the rope that would probably hang him. He had been so happy when he found out how Zach was a braggart and a bumpkin who didn't know when to shut up.
Alas! His superiority complex and his condescending attitude became the things that embarrassed him in front of the people and in front of Clara whom he was sucking up to.