'Pretty Little Liars': Tyler Blackburn and Drew Van Acker Talk Jason Shocker, 'A' Targeting Caleb (Exclusive Video)

Each week, Pretty Little Liars doles out some of the most shocking reveals on TV and its most recent episode was no different, with viewers discovering that Spencer had another sibling: Jason DiLaurentis.

Actors Tyler Blackburn and Drew Van Acker dropped by The Hollywood Reporter cover lounge recently to chat about just what what that means and also preview what's coming up in Monday's episode, "CTRL:A," during which Hanna's boyfriend Caleb becomes the target of "A's" actions.

There were seeds planted all season long in regards to the Jason-Spencer reveal; it was cemented early on that there was something brewing between Jason and Spencer's father. Even so, Van Acker, who plays the new member of the Hastings family, admitted to THR that he himself was "shocked" when he leafed through the script.

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"It's not in the books [by Sara Shepard, of which the ABC Family series is based on]. It's not planned that way and they switched some things around to make that work but I was very shocked," said Van Acker, "but relieved at the same time."

Up until this point, Jason has been referred to as creepy and mysterious, so will viewers see another side to him?

"She (Spencer) always saw him as this creepy older brother/neighbor and now things have taken a turn in a completely opposite direction," he says of upcoming developments.

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At the tail end of last week's episode, it was teased that Caleb would be the unlikely target to "A's" infamous text messages in "CTRL:A." Blackburn, who as THR reported was upped to a series regular for season 3, previewed what's to come.

"Caleb is being accused of some hacking charges that are false, but it lands him in hot water with Rosewood P.D.," he teased. "It lands him in a sticky situation."

Chief among them: interrogations by the police led by Garrett and a team-up with Hanna, who forces Caleb to do something that gives him pause.

"He does not want to do it at all and I understand why," Blackburn reveals. "It's pretty funny."

Pretty Little Liars airs Mondays at 8 p.m. on ABC Family.