It turned out to be Alex Drake, Spencer's long-lost twin sister.
Yeah, you can read all about that here.
With all the insane twists and turns of the show, and the crazy build up of the reveal, it's expected that there would be some not so nice opinions.
But sheesh, Twitter went off.
It got so bad that show creator, I. Marlene King had to step in online.
"To the Emison fans who are asking me to kill myself tonight: You are hateful and do not represent the meaning of 'love is love.' Shame on u."
"I was disappointed in the episode but it's the way that you talked to your fans after that made me lose respect for you," one fan wrote, in which Marlene replied:
"I was greatly disappointed in the way the PLL fans spoke to me. I guess we can agree to disagree."
"For all of you who have sent me hate, I still love you. For those of you who have not, I love you more," she concluded.
Everyone is entitled to an opinion, and when it comes to a long running show that fans have been heavily invested in, it's totally expected... but the death threats and insane commentary over a television show is a bit much...
What did you guys think of the reveal?