Okay...
This. NO. Seriously.
Julian CANNOT BE A HERONDALE. Because that would mean that he and Jace are BROTHERS, and there was never a mention of Stephen Herondale having another child (unless Amatis was pregnant when they got divorced and nobody knew about it)*. But since
Julian is supposed to know all along that he's a Shadowhunter: "The main female protagonist’s name is Emma, the main male protagonist’s name is Julian. They are both Shadowhunters. They both have always known they are Shadowhunters."
So, if Julian always knew he's a Shadowhunter, then most likely he is aware of his parentage? (Even Will is in TID!) Ugh, Cassandra, always plotting an intrigue revolving around the bloodlines. I can't believe I am actually speculating about this when she hasn't even written the book yet, nor do we have a confirmation that another trilogy will be published! OMG this is driving me crazy. "Clockwork Princess" needs to come out now, or I will lose my mind!
*Does it say in CoG that Stephen had siblings? I don't think so. I need to re-read it because I barely remember what happens! (Except for the stuff referenced in CoFA)
P.S. Also,
squee on Jem having babies!!! P.P.S. And no, I do not take it as a confirmation that Jem survives the "Clockwork Princess". At the rate he and Tessa are going in the 2nd book of the trilogy, she might be pregnant in the third... :P
P.P.P.S. Obviously, I'm just kidding. I want Tessa to be with Will. And I want Jem to live, but I think he needs to die - for the sake of making the story more dramatic and believable! (because, you know, that's what's important in a novel about demon hunters)