What do you do when a past client wants to book a time you're holding holding for a meet and greet?

I've had this happen a few times. I have a meet and greet set up in a couple days and I get a call from a repeat client requesting the dates the person for the meet and greet wants. Do you tell your repeat client you have to wait to see if this new person wants the time after the meet and greet or cancel the m&g and give your client the time?