Great tenant but should I be worried about this?

[Jonathan Farber]

I have a tenant who's been in the property for 2.5 years.  He pays on time, agree's to slight rent increases and even makes repairs himself when they are small (he's handy).  He's also a good communicator.  Recently he mentioned he had a friend staying with him in a 3rd bedroom for a few months.  Initially, I brushed it off, as he's been a great tenant but then it interfered with work I was having done on the unit when that 3rd bedroom was needed for access.  At that point, the voice inside started to chime up making me wonder if this was okay or something I should raise an issue over.  Has anyone had this before?  A great tenant who is technically breaking the lease by having an extended guest?  Thanks for all input!