Who Is Charles and the 6 Most Shocking Moments of the 'Pretty Little Liars' Spring Finale

— -- WARNING: If you haven't watched Tuesday night's spring finale of "Pretty Little Liars," there are major spoilers for the episode and the entire series below.

When we last left Spencer Hastings, Aria Montgomery, Emily Fields and Hanna Marin, the four pretty little liars were being arrested as accessories to Mona Vanderwaal's murder.

In the aptly-titled finale, "Welcome to the Dollhouse," the girls find themselves in a life-sized dollhouse created by "A," the unnamed character who's been sending threatening messages to the liars throughout the series.

As Spencer, Aria, Emily and Hanna attempt to make sense of what A's plan is, Spencer's boyfriend Toby Cavanaugh, Hanna's boyfriend Caleb Rivers and Aria's ex-boyfriend Ezra Fitz team up with Spencer's parents to try to find out what has happened to the girls when their van goes missing on the way to the prison.

While all of the above action sounds like a drama-filled hour alone, "Welcome to the Dollhouse" also gives the fans long-awaited answers to a few of the series' most burning questions. Check out the most shocking moments from the finale below:

1. Mona is alive!

Despite never finding her body, Mona was presumed dead by police, who spent this season trying to find her killer. Spencer, Aria, Emily and Hanna also believed she was dead, and viewers were shown Mona's body in the trunk of a car.

However, in Tuesday's finale, the liars encounter a girl dressed like Alison and wearing a mask of Alison's face. She then takes off her mask to reveal she is Mona and not dead after all. It turns out A faked Mona's death and was keeping Mona trapped inside the dollhouse.

Aria helps confirm Mona's identity in one of the episode's few lighthearted moments:

"I didn't think you were wearing [those orange prison jumpsuits] to make a fashion statement," Mona tells the girls.

"Yep, she's Mona," Aria says.

2. Spencer's parents learn that A is still threatening the girls.

When Mona was identified as the anonymous character making the liars' lives difficult, Peter and Veronica Hastings thought their daughter Spencer and her friends were finally safe. But they didn't know that a new A had taken over and continued the game.

With nothing to lose, Alison, who was found guilty by a jury for Mona's murder, reveals to Spencer's parents that A has continued threatening the girls all along.

While the police believe Spencer, Aria, Emily and Hanna have escaped on the way to prison, Spencer's parents turn to Toby, Caleb and Ezra to find out what really happened to the girls.

3. Lieutenant Tanner finally discovers the truth about A.

For much of the season, police lieutenant Tanner appeared to be suspicious of Spencer, Aria, Emily and Hanna.

In the spring finale, Tanner even has Caleb brought in for questioning, believing he helped the girls escape on their way to prison.

But with Spencer's parents as his lawyers, Caleb is able to convince Tanner to allow him to help find the girls using his computer hacking skills. He finds the location of the van the girls were riding in.

Tanner, Caleb, Toby, Ezra and Spencer's parents head to the van's location, where Tanner and Toby find A's lair.

4. Andrew Campbell is listening to Spencer's mom's phone call.

Though he has helped the girls in the past, Andrew appears suspicious to viewers, such as when he tells Aria that the world may be better off without Mona.

Viewers are given even more of a reason not to trust Andrew, when he is shown listening to the phone call between Spencer's mom and Spencer's sister, Melissa Hastings.

5. A has a soul.

As the girls make their escape, Spencer finds a movie room decorated with family photos.

A projector turns on and plays a family movie with Alison and Jason DiLaurentis' mom, Jessica DiLaurentis, who was killed by A, and three children.

Mona walks in and, picking up a family photo, says, "This is not at all what I thought it would be - A has a soul."

6. #CharlesIsA

It turns out the big A reveal of the spring finale -- as indicated by the hashtag #CharlesIsA that appears during the episodes final moments -- is that Charles is A.

Spencer is the first to figure it out when she rearranges the playing blocks in the game room to spell Charles.

At the prom A makes them set up, the girls call out the name "Charles" to a male figure who then appears. And as Spencer watches the home movie with Jessica DiLaurentis, the male figure appears again next to her. Spencer asks him if he is Charles, but Mona enters before he replies.

But who is Charles? Fans will have to wait until the next season to find out.