What was Ben Armstrong's illness?

Excuse me, but I'm curious to know more about the health condition of Ben Armstrong. Could you please elaborate on what specific illness he was diagnosed with? I understand that privacy is important, but if it's not too personal, I'd appreciate any information you can share regarding his health status. It's just that I've been following his career closely and his sudden departure from the public eye due to illness has left many of us concerned and wondering.