You use frankly when you are expressing an opinion or feeling to emphasize that you mean what you are saying, especially when the person you are speaking to may ...
I can frankly say is a correct and usable phrase in written English. You can use it when you want to emphasize that you are being honest and direct in ...
Quite frankly, the thought of it terrified me. People say this is a selfish society, but frankly I've seen too much kindness, self-sacrifice and generosity ...