The character Mona Vanderwaal is revealed to be "A," the anonymous antagonist in the Pretty Little Liars series, starting in the TV show around the middle of season 2. This reveal occurs in the episode titled "Unmasked," where it is disclosed that Mona was the original "A" tormenting the protagonists. This storyline is aligned with her introduction as "A" in both the TV adaptation and the book series. Mona's role as "A" and the timing of this reveal in the series is well documented and recognized as a significant plot twist in the Pretty Little Liars franchise.
