What the hack? You don't know about this for 2 years?

I guess that you are not on top of your rental business and rental market.  

1. You can terminate the lease based on whatever you have agreed with him that he can not rent out the property, etc.  

2. Just pretend that you don't know anything about this and keep collecting your rental.  One thing you can do is to raise the rent to increase your profit and cut into his profit.