So... Jason's Peter's kid, right? Do we just assume that now? I get so worried and ramped up trying not to think too hard about these kinds of things, because if you're right you accidentally ruined it for yourself and even if you're wrong you still get people up your ass about spoilers no matter how stringently you couch it as speculation, but then on the other hand this show makes not even a little bit of sense, on a delirious and fundamental level, so there's not really harm in speculating: If he's Spencer's half-brother, what of it? Won't matter.
It won't even be the big deal, it'll turn out that actually Ali's firecracker never went off, and it was actually Jason who accidentally blinded Jenna with his reckless use of a measuring tape, just let go at the wrong moment and zoom, or that actually it's Mike Montgomery that is Aria's father with Jackie Molina or something.
Yeah, Jason is Peter's illegitimate son with Drunk Alison's Mom, but did you know that he is also Alison and there is no Alison and he would sometimes put on a blonde wig and pretend to be a high school bitch just so he could get to know his sister Spencer? Apparently the constant stress of making out with his best friend Ian while in disguise as his imaginary sister got to be too much, so he murdered the Alison identity and tried to pin it on Toby, but Jenna was already pregnant with Toby's Fremen baby so Garrett had to step in to save them, and all of this was caught on tape by the NAT Club, who subsequently diced up the film and buried it in sixty-four canisters around town in locations that correspond to the freckles on Alison's back that only Emily can remember.
Jason: "Does 'she' know?"
Peter: "No. And 'she' is not gonna find out tonight. And that could literally mean anything! Pronouns are like crack for this show! You shouldn't be here!"
SCARY BARN: LIKE NOT THAT LONG AGO, AT THIS POINT
Emily: "Wow, almost dying all the time is hard on a lady."
Liars: "Look, a nondescript shovel leaning against a wall! So suspicious! And taped to it are some GPS coordinates! I bet they correspond to the location of those Tory Burch boots!"