Ive never been in this situation but discretion would seem to be the rule here. A smile or a nod or just nothing would all make sense.

I did have a situation slightly different where i was dating a girl much younger than me. We were at a bar on vacation and someone else who had been over-served made a comment “she must be his sugar baby”. Which was true. I didn't miss a beat and said “actually she’s my dominatrix” also true. No one was expecting that. That was a fun time.