S7: Did Lucas ever explain how he didn't connect Charles DiLaurentis to Alison DiLaurentis? Seems like nuclear level cognitive dissonance.

In S7, when Emily and Hanna confront Lucas about his friendship with Charles DiLaurentis, what does he say? Specifically, does he ever explain how he didn't connect Charles DiLaurentis to Alison DiLaurentis, given that he knew both of them? That level of cognitive dissonance seems impossible. What's his explanation?