Perhaps Prince Sylvain wasn't as reckless as he used to be and somebody might have told him to have some restrain as well as how to maintain an ambiguous expression. However, it was hard to miss the slight shift of emotion in his eyes when he was met with the duke's compliance.
Since The Great One had given him a chance, then he would gladly take the stage. Everyone had done their part and he had been itching to join the performance. No matter what, he couldn't forget the look on that person's eyes when they had first met and how they had treated him after.
Yes, he admitted that compared to that person, he was nothing at all. Not even worth a strand of their hair. Still, they should've been equal because that person needed him as much as he needed them. Yet, they looked at him as if he was a mere puppet.