This story contains spoilers for the first five episodes of “Agatha All Along.”

The identity of Joe Locke’s mysterious Teen has finally been revealed: He’s been Billy Maximoff all along.

The fifth episode of “Agatha All Along” sees the boy who could not be named confront Agatha (Kathryn Hahn) for killing Alice (Ali Ahn), the protection witch who was trying to save her, during their just completed trial. He is disillusioned that all of the witches in their ragtag coven are operating just for their own agendas.

“You’re so much like your mother,” Agatha says to the distraught boy. As he unleashes his blue-colored magic, it’s clear she is referring to Wanda Maximoff, the Scarlet Witch.

Episode 5 ends without mentioning the teenager’s name. But Marvel Studios’ recent promotional materials have not shied away from confirming that, as long speculated, Locke’s Teen is indeed Billy.

Here’s everything you need to know about Billy and his backstory.

Who is Billy Maximoff?

Billy Maximoff (Julian Hilliard) first appeared in “WandaVision.”

(Marvel Studios)

Young Billy Maximoff was introduced in “WandaVision” Episode 3. After becoming mysteriously pregnant, Wanda gives birth to twins Tommy and Billy less than 24 hours later.

The magically created siblings have an equally accelerated childhood. The infants turn into 5-year-olds in less time than it takes to put a baby down for a nap. The kids later age themselves into 10-year-olds instantly — so they can have a puppy.

Tommy and Billy eventually show that they’ve inherited specific Maximoff traits. Tommy, taking after his uncle Pietro, can move at superhuman speed, while Billy shares Wanda’s magical abilities.

But the twins, like the version of their father Vision that lives with them in Westview, were created by Wanda’s reality-altering chaos magic. During her showdown with Agatha, Wanda realizes she can’t keep forcing an entire New Jersey suburb to live out her fantasy. After putting Tommy and Billy to bed one last time, Wanda undoes the magical hex controlling the town and the twins dissolve along with their dad because they can’t exist without it.

A grief-stricken Wanda meets a Billy and Tommy from an alternate dimension in “Doctor Strange in the Multiverse of Madness” (2022).

What were the clues that Teen was Billy all along?

Agatha (Kathryn Hahn) referred to him as Teen (Joe Locke) because a magic sigil kept his identity a secret.

(Chuck Zlotnick / Marvel)

While Teen’s identity was a magical secret during the first episodes of “Agatha All Along,” there were plenty of hints (and red herrings) leading up to the big reveal.

Teen looking for Agatha and helping break her out of Wanda’s spell gone wild in Episode 1 was the earliest indicator that he already possessed some magical skills. Even Agatha teases he must already be plenty powerful to break a spell cast by the Scarlet Witch.

It became even clearer that there was more to Teen than meets the eye when a magical sigil prevented Agatha (and the audience) from hearing his name in Episode 2. The symbol that appeared over Teen’s mouth resembled an M, so one theory held that it stood for Maximoff. (Another suggested that the M is for Mephisto, who gets a mention in Episode 3, but more on that later.)

In Episode 3, Teen, who is 16, shares with Alice that a lot happened to him when he was 13. “Agatha All Along” is set three years after the events of “WandaVision,” which means Teen would have been 13 when Wanda’s hex was active.

The number of teenage boys with an affinity for magic, a possible affiliation with the Maximoffs (or Mephisto), a boyfriend and a connection to Agatha Harkness is pretty limited in existing Marvel lore. It was long speculated that Locke had been cast to play Billy.

The series had also teased the possibility that Teen could be Agatha’s son Nicholas Scratch. But Rio tells Agatha in Episode 4 that Teen isn’t her son, and in Episode 5, Teen says “Nicholas Scratch” for all to hear. By the time the Teen wields his magic, all signs point to him being Billy.

So who is Wiccan?

There’s more to Joe Locke’s teenage wannabe witch than meets the eye in “Agatha All Along.”

(Chuck Zlotnick / Marvel)

In the comics, Wiccan is the superhero alias used by Billy Kaplan. Initially going by the code name Asgardian, Kaplan was introduced as a member of the Young Avengers whose magical powers include blasting energy and manipulating reality.

Kaplan and his Young Avengers teammate Tommy Shepherd, a.k.a. Speed, eventually learn they are the reincarnations of Wanda and Vision’s twins, Billy and Tommy Maximoff.

Comic book Wanda becomes pregnant after she and Vision have a run-in with a group of witches — who happen to be the grandchildren of her mentor, Agatha Harkness — that involves her having to channel a giant amount of magical energy. Doctor Strange later helps deliver Wanda’s babies.

Eventually a villain named Master Pandemonium, an agent of the demon lord Mephisto, comes after the infant twins. Long story short, the twins are revealed to have been (at least partially) created from lost fragments of Mephisto’s essence and he reabsorbs them.

But it turns out Wanda’s magic affected the fragments enough that they break free from Mephisto and their souls are reincarnated into separate families.

Comic book Billy Kaplan is Jewish and is in a romantic relationship with Teddy Altman, a.k.a. Hulkling.

The Marvel Cinematic Universe has already introduced a number of Billy’s Young Avengers teammates, including Kate Bishop (“Hawkeye”), Cassie Lang (the “Ant-Man” films) and America Chavez (“Doctor Strange in the Multiverse of Madness”). Plus, Kamala Khan is seen recruiting for a new superhero team at the end of “The Marvels.”

But what about Tommy Maximoff?

Twins Tommy (Jett Klyne), left, and Billy (Julian Hilliard) with their mother Wanda Maximoff (Elizabeth Olsen) in an episode of “WandaVision.”

(Suzanne Tenner / Marvel Studios)

If Billy survived the events of “WandaVision,” there is a good chance Tommy did as well. Could Billy be trying to find him?

In Episode 2, when Billy tells Agatha that he wants her to take him on the Witches’ Road, he mentions that “the Road promises that what’s missing awaits you at its end.” At the time, it was implied he wanted more power, but considering the amount of power he has been shown to possess since, perhaps what he is looking for is his missing family. Viewers will have to wait and see if a reunion with Tommy and/or Wanda is awaiting Billy at the end of “Agatha All Along.”