He's been Triggered !
After you’ve had chickenpox as a child, the virus lays dormant in your body. A strong immune system usually keeps the VZV in check. It’s when your immune system becomes compromised or is weakened, however, that triggers the VZV to reactivate and cause shingles.
https://www.medicinenet.com/what_triggers_a_shingles_outbreak/article.htm