"And frankly, you know what?"
Translation:Et très franchement, vous savez quoi ?
I really don't think it is necessary.
I'm not going to be super clear because it is quite subtle, but let me try to explain how they can be (very slightly) different sentences. Without the "très" the meaning can shift a little between "frank/honest/candid" and "plain/without complications". I realise these are close, but the former relates to an entity capable of being dishonest and choosing not to, while the latter can be used for things as well. That's the meaning that's behind eg "zone franche" or "franc de port", where it is about the absence of taxes or additional regulations.
So the version without "très" could mean either "i'm going to tell you my most honest opinion on the matter right now" or possibly "i'm going to tell you what the matter is all about if we get to the point and forget about all side issues". The version with "très" kind of discards that second option, for reasons i can't fathom.