who's first law or psychology?

If a lawyer who masters the clinical psychology and finds himself forced to stand face to face with an accused who was one of his patients ...

How should he act?

Is it according to his professional confidentiality or according to his job as a lawyer which obliges him to defend his agent until the end without thinking of any other details.?

And since he has all the truth about his adversary, especially if this patient has any psychological disease that only him(the lawyer) knows about it ?

And what if this illness makes the accused innocent?

where are the limits ?