How to respond to a comment asking about 2 characters who don't appear in the fic?

This morning I woke up to a comment saying "Wonder what X and Y are doing?"

I have no idea how to respond. The fic doesn't name them, and tbh... I barely know who they are. I do know that they are related to the characters I wrote about, but that's it.

How do I respond? I've been thinking of potential replies but I genuinely cannot come up with anything!😔