What action would you have him take?

And honestly, we are all human and all of us make mistakes. Having an affair is usually something that should be resolved privately, in your personal life, not in public. The business context of this affair is clearly something he wasn’t aware of at the time and punishing him for being deceived seems extreme.

So because he was tricked he must resign ?

Fool me once shame on you… fool me won’t get fooled again.