That's quite a large increase, which is the problem with not doing regular increases. If you tell a tenant every year that the rent is going up by $25 or $50, they usually don't bat an eye. When you tell them it is going up $150, especially when that's a pretty significant percent of the cost, it is more likely to ruffle feathers. That's why we raise the rent to near FMV each year, rather than putting it off and then surprising them with an unexpected large increase. They are more likely to resent a large increase than they are to appreciate no increase at all up to that point. For most people, raising the rent $25-$50 most years is going to be barely noticed.
I'd reach out, explain that you think they are a fantastci tenant so you've skipped any increase but that with yur rising costs, you simply can't do that this year. Tell them that you need to rais it to $1250, and are giving them plenty of notice to help it out. Point out that you value them and want them to stay, and hope that this works. IDK if I'd mention, or not, that if I were listing it for a new tenant, it would probably be at $1500.
Yes, you don't want to lose them, but if this is truly that far under FMW, they don't want to lose you, either. Sure, there's the possibility that they will become more high-maintenance, but that's probably work an extra $150/mo. (If $1100 was a competitive rate 8 years ago, my guess is that even $1500 is below MV now. Tha't only about 4% annual increase, which seems low, given what housing and inflation have seen during that time.)