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Who Is 'A' On 'Pretty Little Liars?' Keegan Allen Knows And He's Telling Us All About It

Someone's got a secret.

Keegan Allen knows all sorts of secrets about "Pretty Little Liars" -- including "A"'s identity.

We already know that the big "A" reveal will happen before the start of season seven, and according to Allen, prepare to be shocked. Speaking to MTV News, Allen doesn't exactly expose the Big Bad's identity, but he does tell us how Marlene King broke the news to him after years of begging and how stunned he was by the big reveal.

"If you go all the way back to season one... and you really pay attention to every clue, you can figure it out," Allen said. "It all makes total sense."

Allen's pretty little co-star Lucy Hale recently revealed that she was the only Liar who didn't know "A"'s true identity, but he said, "That's not true." (Do you know who also lies, Hale? Big "A." Maybe those "Aria is 'A'" theories do hold some weight after all.)

"Lucy probably knows! She's just really charming," Allen said. "I think that's why she's shying away from it. But we all have this pact where we don't want to tell anybody."

As for the big season five finale, Allen has one word for it: "Unsettling."

He added, "It will keep you up at night... you guys asked for it!"