"What gave it away?" Gerhardt mysteriously smiled at that question, before he genuinely answered.
"Young folks such as yourself have an air of honesty about them. Even if you would lie I'd still be able to smiff out the truth from your demeanor and actions." He answered. "Masking one's feelings is not something everyone can do. Many attempt at it, some bluff their way through and others attempt to divert the attention away from it, but truly masking one's self is rare.
The best at it are the magicians, sure to the common eye they perform simple parlor tricks that when the trick is explained, the magic and mystery is broken. 
What they don't see is half of that trick. The perfectioning of movement, the stillness of one's expression to not give away the truth of the matter. Routine. To live one's craft and to become the act."
He continued his prepared talk, knowing the young brash prince would need it.
They were far from the safety and familiar walls of his Kingdom.
He took in the young prince's responses, knowing full well the displeasure some of his words caused. Still, play time was over. He had to grow up and become the man he was destined to be or Belisio would suffer even longer.
Gerhardt sighed. 
Uilles had always been better at this. The old Knight had always managed to garner respect and favour by just showing up.
Sometimes Gerhardt had thought it quite unfair.
Especially knowing what the young prince's intentions had been.
Uilles would have been a better mentor than he.
Still, no use going back to burned down bridges, not when it was time to move forward.
The boy's immediate retaliation made Gerhardt think he'd hit a nerve somewhere.

"What do you take me for?" Corvo scoffed as he set his cup of Brenwyn down, unfinished. "After everything that's happened, nothing could be further from my mind. In any case, allow me a moment to get dressed... and call me Duncan."
Gerhardt turned his eyes on him again.
"I take you for a young man in his prime. You have urges just like the rest of us, to procclaim otherwise would truly be foolhardy and stupid. Consider it merely a friendly warning and reminder, Duncan. Many a strong and loyal heart have fallen the moment they met the 'right' pair of 'fine eyes'. Just know that should you want company, you'd better pay for it. That way it is strictly business and you can be assured he or she is only interested in your coin."