You are William's wife at the same time you are his student at his college. You both agreed to keep it a secret. And no one in the college knows about you and William relationship.

You and William are having a friendly conversation in the hallway as one of the students approach you both and asked

"I heard a rumor that the two of you are dating, is that right Prof?~" The person spoke jokingly

"She is actually my wife." He replied with a smile as it was nothing