The biggest mystery in Season 4 of The Flash has nothing to do with Savitar or any other new villain, but instead on a seemingly innocent girl that pops up every now and then to spread awkwardness and her oppressively sunny disposition. Actress Jessica Parker Kennedy plays a character literally billed as “Mystery Girl” that debuted during “Crisis on Earth-X” at Barry’s wedding, and we’ve got an outlandish new theory about her true identity:

What if she’s a gender-bent version of Barry’s grandson from the comics, Bart Allen?

In every one of the Mystery girl’s three appearances on the show thus far, she comes off as a jittery, overexcited mess. Her behavior implies that she has some kind of nostalgic pre-knowledge of Barry Allen and the rest of Team Flash, which is why everyone thinks she’s a time-traveler. If that were the case, then it would make perfect sense for her to have a backstory just like Bart Allen’s, especially how his character appears on the animated series Young Justice.

Bart Allen, aka Impulse, on Season 2 of 'Young Justice'.
Bart Allen, aka Impulse, on Season 2 of 'Young Justice'.

In Bart Allen’s first DC Comics appearance in Flash #92, he suffered from a hyper-accelerated metabolism, so his grandmother brought him back in time to the present-day to work out a cure with Wally West, who was The Flash of that time. The Young Justice version of Impulse, however, is quite different, and his personality bears a striking resemblance to the Mystery Girl’s

The Mystery Girl first showed up at Iris and Barry’s wedding disguised as a deeply sentimental and overenthusiastic caterer. Then she bumped into Cisco and Ralph in Jitters during “The Elongated Knight Rises”, when we saw her scribbling the same strange symbols that Barry did after he emerged from the Speed Force.

But most recently, she met Harry and Caitlin in Jitters at the end of “Enter Flashtime,” and showed a more serious, potentially even villainous side to her character.

It’s become clear that she’s not just a time-traveling voyeur — if she even is a time traveler — and that she has a much more serious mission in mind.

The Mystery Girl on 'The Flash' has a dark side.

We’ve seen an almost identical character arc from Bart Allen Season 2 of Young Justice, subtitled “Invasion” because of the imminent alien invasion and subsequent apocalypse, the same one that he travels back in time to prevent.

In the sixth episode of Young Justice Season 2 — “Bloodlines” — a time machine emerges right in the middle of Mount Justice, and out pops Bart Allen. After evading a couple Robins and Beast Boy, the first thing he does is go and find Barry Allen to give his grandfather a hug and prevent The Flash from dying. Their initial meeting feels really dopey and sentimental in the same way that Barry’s first meeting with the Mystery Girl did on The Flash.

Impulse becomes a series regular in Young Justice after this, and he’s constantly chattering in an animated, silly manner. The Mystery Girl’s behavior is deeply reminiscent of this, as if they’re both a kind of speedster whose brain moves faster than their lips can keep up.

Impulse teams up with his grandfather on 'Young Justice'.
Impulse teams up with his grandfather on 'Young Justice'.

We eventually learn in Young Justice that the entire reason Impulse traveled back in time was to prevent the alien race known as the Reach from utilizing Blue Beetle to take over the world. Bart thought that going back and saving The Flash might prevent the apocalypse from ever happening. His “actual” personally is grave and jaded with his giddy persona something he adopted to gain favor with the heroes of the present day.

Could that be exactly what the Mystery Girl is trying to do on The Flash? Her third appearance did imply a more serious personality than whatever act she’s been putting on all this time.

For all we know, maybe the Mystery Girl is from a similarly dark future, and her seemingly manic personality is all a ruse to hide the truth from Team Flash. She could be waiting for the perfect moment to reveal the truth about what’s coming for them all.

Bart Allen in 2056 tinkering with his time machine on 'Young Justice'.
Bart Allen in 2056 tinkering with his time machine on 'Young Justice'.

Come to think of it, Blue Beetle would make a great addition to The Flash Season 5. Loosely adapting Young Justice Season 2 could be an interesting next step for The CW, even if it’s just 2018’s next big crossover event. Otherworldly invasions seem like the status quo for these events.

Generally speaking, the evidence is there that the Mystery Girl is a time-traveler related to the Allens somehow. The most popular theories about the Mystery Girl’s identity assume she’s Iris and Barry’s daughter, Dawn Allen, or even their granddaughter Jenni Ognats. But these are the obvious theories that have already been shot down.

In an interview with TV Guide published last week, The Flash executive producer Todd Hellbing said that fans hadn’t correctly guessed the Mystery Girl’s identity just yet: “Every year there’s theories all over the place about what we’re doing and some of them get pretty close, some of them they hit like one part of it but they don’t get other parts, so it’s fun to read. I don’t think anybody ever is going to guess exactly what it is.”

Maybe we’ve just successfully guessed “exactly what it is” with this new theory? We’ve only got seven episodes left in The Flash Season 4 before we find out for sure, so it’s about time The CW started setting up Season 5. Mystery Girl’s bound to play a part in some way.

The Flash airs Tuesday nights at 8 p.m. Eastern on The CW.