Sounds like this CTO will have more support than you. Time to move on. Don't understand why everyone is talking lawyers. I'm sure that you have an equity stake

Sounds like this CTO will have more support than you. Time to move on. Don't understand why everyone is talking lawyers. I'm sure that you have an equity stake which value will be helped by this new CTO. If you have no equity and (as you say) are a founder, then you are out-of-luck and no legal magic can solve this. Move on and leave on good terms. You never know.