How do i trigger the cutscene with Dorian's Letter?

if I remember right you have to be super friendly and stuff with him. Also get to know everything about him too. I am not etirely sure but maybe you may need to talk to mother gisselle too(?) because I know at one point she walks into the throne room asking you to speak to her. talk to her and she says she has a private letter that is only for Dorrian. You can defend him if you wish but she insists that you bring the letter at least to him. I usually take the option that I will show him the letter which she's wishy washy about. i go over to Dorrian and classic Dorrian thinks it's from a admirer, love interest, some ordinary girl that is into him. Your character tells the truth and he's like "Wait let me see". This kicks into the cinematic about it's from his dad and he's balistic on how his dad didn't bother to show in person blah blah blah.

Mother Giselle is involved, she gives you the letter if I remember correctly. On one playthrough I got this quest pretty early, but I'd been getting my full education on Tevinter politics back in Haven, and I chose mages so we had our

On my second playthrough I've not given him any special attention and chose templars, and I didn't get the letter yet. 

Yeah above poster is right. I did it exactly the same way and second I chose templars and I havent got him yet and at the point before skyhold, no spoilers.

Odd....On my first playthrough I kept socializing with Dorian and mother gizzelle and even went Templars and she still showed up, wanted to have to give the letter over to him and as i did in one of my recent characters I defended him but still promised to give the letter and still gave the letter to him and blah blah blah blah about his father.

Hmmmmm.....I know Dorian has a couple WAR TABLE ONLY missions (One in Fereldan and the other in orlias) and has a couple missions where you have to explore but I believe one of his explore and kill stuff is after the whole (spoiler free) thing then you'll get a mission called "ONE LESS VENETORI" where you have to take Dorian out to kill Venetori soldiers because of (spoiler free) after the (spoiler free) meeting.