Pretty Little Liars' Keegan Allen knows who 'A' is.

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Unfortunately, the actor isn't about to spill the beans.

"I found out!" Allen (Toby) told Spoiler TV. "It was pretty mind-blowing."

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The ABC Family series will reveal the killer's identity before season 7 opens, but fans still have to wait almost a season and a half for the truth. According to Allen, its definitely worth the wait.

"I think it's genius. I think it's 100% incredible," Allen said, according to Spoiler TV. "It's mind-blowing and in the way that it comes to form, the whole storyline of this and it's explained. It explains everything in such a classy way and also in a way that makes it feel like history in the making."

In the meantime, fans can catch up with the Liars this December for the series' first-ever Christmas special. The holidays won't b overly jolly for the Rosewood crew, however, what with Spencer's murder charge, Toby's broken leg, and 'A's unwelcome appearance at the Ice Ball.

Find out more when Pretty Little Liars airs Dec. 9 at 8 p.m. ET on ABC Family. Click the video below to see a preview.

Tags: pretty little liars ABC Family television