A key/fingerprint change occurred on a friend's server to which I have access. So I text him and ask, "Did you change the certificates?" upon which he answer "Yes".
My initial thought is then to update my local fingerprint, but then it occurred to me: What if someone does a MITM attack simultaneously as my friend has done this legitimate change?
How do I proceed to make sure I'm not being tricked?
PS! In this particular case, my friend went from a self-signed certificate to using Let's Encrypt, but answers should reflect any situation involving a change of fingerprint.