This story contains spoilers for the first five episodes of “Agatha all the time.”

The identity of Joe Locke's mysterious teenager has finally been revealed: he was Billy Maximoff all along.

In the fifth episode of “Agatha All Along,” the boy-who-couldn't-be-named confronts Agatha (Kathryn Hahn) about Alice (Ali Ahn), the guardian witch she wanted to save, during her just-completed trial killed. He is disillusioned that all the witches in their motley coven only pursue their own goals.

“You are so similar to your mother,” Agatha says to the desperate boy. When he unleashes his blue magic, it is clear that it refers to Wanda Maximoff, the Scarlet Witch.

Episode 5 ends without mentioning the teenager's name. But recent promotional materials from Marvel Studios haven't shied away from confirming that Locke's Teen is, in fact, Billy, as long speculated.

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 episode 3 of WandaVision. After Wanda mysteriously becomes pregnant, she gives birth to twins Tommy and Billy less than 24 hours later.

The magically created siblings have an equally accelerated childhood. The infants become five-year-olds in less time than it takes to put a baby down for a nap. The children will later immediately turn 10 years old – so that they can have a puppy.

Tommy and Billy eventually reveal that they have inherited certain Maximoff traits. Tommy is modeled after his uncle Pietro and can move at superhuman speeds, while Billy shares Wanda's magical abilities.

But the twins, like the version of their father Vision who lives with them in Westview, were created by Wanda's reality-altering chaos magic. During her showdown with Agatha, Wanda realizes that she can't continue to force an entire New Jersey suburb to live out her fantasy. After putting Tommy and Billy to bed one last time, Wanda lifts the magical curse controlling the city and the twins disband along with their father because they cannot exist without him.

A grieving Wanda meets Billy and Tommy from another 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 magical seal kept his identity secret.

(Chuck Zlotnick / Marvel)

While Teen's identity was a magical mystery in the early episodes of Agatha All Along, there were plenty of clues (and red herrings) leading up to the big reveal.

When Teen searched for Agatha and helped free her from Wanda's spell in Episode 1, this was the earliest indication that he already had some magical abilities. Even Agatha teases that he must already be powerful enough 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 seal prevented Agatha (and the audience) from hearing his name in Episode 2. The symbol that appeared over Teen's mouth resembled an M, which is why one theory suggested that it stood for Maximoff. (Another suggested that the M stands for Mephisto, who is mentioned in Episode 3, but more on that later.)

In Episode 3, the 16-year-old teen tells Alice that a lot happened to him when he was 13. “Agatha All Along” takes place three years after the events of “WandaVision,” meaning Teen would have been 13 when Wanda's Hex was active.

The number of teenagers with an affinity for magic, a possible connection to the Maximoffs (or Mephisto), a friend, and a connection to Agatha Harkness is fairly limited in existing Marvel history. It has long been speculated that Locke was cast in the role of Billy.

The series had also hinted at the possibility that Teen could be Agatha's son Nicholas Scratch. But Rio tells Agatha in Episode 4 that Teen is not her son, and in Episode 5 Teen says “Nicholas Scratch” for everyone to hear. When the teenager uses his magic, all signs point to him being Billy.

So who is Wicca?

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

(Chuck Zlotnick / Marvel)

In the comics, Wiccan is the superhero alias used by Billy Kaplan. Originally codenamed Asgardian, Kaplan was introduced as a member of the Young Avengers, whose magical powers include energy blasting and reality manipulation.

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

In the comic book, Wanda becomes pregnant after she and Vision run afoul of a group of witches – who happen to be the grandchildren of her mentor Agatha Harkness – which results in her having to channel a huge amount of magical energy. Doctor Strange later helps deliver Wanda's babies.

Finally, a villain named Master Pandemonium, an agent of the demon lord Mephisto, is after the little twins. Long story short: it turns out that the twins were created (at least in part) from lost fragments of Mephisto's essence and he reabsorbs them.

But it turns out that Wanda's magic has influenced the fragments so much that they break free from Mephisto and their souls are reborn into separate families.

Comic book writer Billy Kaplan is Jewish and is romantically involved with Teddy Altman, also known as 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” ). Kamala Khan is also 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's a good chance Tommy survived too. Could Billy try to find him?

In Episode 2, when Billy tells Agatha that he wants her to take him on the Witch's Road, he mentions that “the road promises that what is missing will be waiting for you at the end.” At the time, it was implied that he had more power wanted, but considering how much power he's wielded since then, perhaps what he's looking for is his missing family. Viewers will have to wait and see if Billy will be reunited with Tommy and/or Wanda at the end of Agatha All Along.