How to read message by someone who unfriended me?

I had a rather odd occurrence.  Someone who was my friend in the game sent me a message while I was battling someone else and it quickly appeared at the top of the screen but I did not get a chance to read it because I was into my current battle.  Then when I was done with my battle, it looked like the person was no longer my friend.  The game (app on Android) tells me I have messages, but I cannot access them because the person is no longer my friend.

So, either I am looking at resetting the message count to 0 because I cannot access it, or figure out how to access this message by someone who is no longer my friend. I think it is some kind of troll and I did not do anything to upset anyone else.