Mentioning an author in query letter

I'm fairly sure it's not a bad thing to mention an author an agent reps in the query letter, but here's the thing: The agent I was going (still will) to query only repped this author for one book. Said author signed with another agent immediately after the first book was published. I realize this happens for a variety of reasons, but since the author is no longer with the agent, should I mention it at all? Don't want to hit a sore spot (if that were the case). Thoughts?