本当のことを知ってたら、あなたにお話しましたよ。

、。

If I had known the truth, I would have told you.

Literal

True [possessive-の] thing [object-を] knew-[conditional-てたら], you [target-に] told [informative-よ].

知ってたら (casual 知っていたら) is a counterfactual conditional — 'if I had known.' お話しました uses the polite お~する form. The sentence is a past counterfactual: the speaker didn't know, so didn't tell.