@REDS
he just litterally said that he'll do a coup man
He said 'coup de grâce', which literally means to strike a final killing blow. The coup you're referring to is 'coup d'etat', which means, an armed insurrection against a ruling regime.
He means that the marquis will shake up the nobles' power, and he would land the final hit.
In
this context, the result is the same , but just wanted to point out the difference.