What is the meaning of "Betraying the slightest suggestion of a smile" in this paragraph:
Rostov asks, “What is the meaning of this, Captain?”
The captain, who seemed mildly surprised by the question, had the good training to maintain the evenness of his affect.
“I am here to show you to your quarters.”
“These are my quarters.”
Betraying the slightest suggestion of a smile, the captain replied, “No longer, I’m afraid.”
The above paragraph is from the novel named A Gentleman in Moscow by Amor Towles.