'The Flash' Boss Reveals All About the Big West Family Secret and That Surprising Reunion

The CW

The West family is about to go on one heck of a roller coaster ride.

The Flash
unraveled a family secret on Tuesday’s episode that will reverberate throughout the rest of the season and threaten bonds. At first it seemed Joe West’s ex-wife, Francine, wished to reunite with her daughter, Iris, but she had other motives. The former drug addict was sick with MacGregor’s disease (a subtle callback to Arrow) and Iris discovers one mother of a secret through her investigative digging: She has a brother.

“That’s Wally,” executive producer Andrew Kreisberg confirmed following a recent screening of “The Fury of Firestorm.”

WATCH: 'The Flash' Stars Dish on Firestorm 2.0 and Ronnie Raymond's Possible Return

Now, the introduction of Wally West isn’t a secret – in August, Aussie actor Keiynan Lonsdale snagged the coveted role of the new Central City speedster, who will debut in a future episode.

“We always knew we were leading up to this, and rather than them suddenly having some cousin that inexplicably [appears]… We always hated on TV shows and somebody’s like, ‘Well, cousin John’s coming!’ And it’s like, ‘Good ol’ cousin John!,’ who no one mentioned before,” Kreisberg said, adding, “The notion that they didn’t know Wally was sort of where that came from.”

Iris now finds herself in a similar position Barry was in last season -- when he kept his Flash identity from her for an extended period of time -- as someone who is aware of a game-changing secret not even her father is aware of.

“Iris is now in the position that Barry was in last year,” Kreisberg explained. “She’s keeping a secret to protect somebody and she’s going to find that -- for all her anger at Barry and Joe from last year -- keeping this secret is not going to be so easy.”

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“It’s going to be weighing on her before she finally decides to take some action in an upcoming episode,” he added.

If there was doubt that Wally could have been fathered by another man after Francine abandoned the family, Kreisberg shut down any speculation.

“[It’s] Joe’s son,” he said.

As for the face-to-face showdown at the end of the hour between Earth-Two’s Harrison Wells and Barry Allen (after a “Did that just happen?” moment with King Shark), we’re just scratching the surface on that awkward “reunion.” In fact, we may even get a glimpse from Wells’ perspective. 

“The next episode opens in a slightly surprising way,” Kreisberg hinted. “This scene will play out, but how it unfolds in [episode] five [“The Darkness and the Light”] is really exciting. You’re going to get a lot of answers to questions you have.”

And, spoiler alert, Wells won’t be the only doppelganger we’ll be meeting as the season progresses.

“It’s about to go doppelganger-a-go-go on the show,” Kreisberg teased. “With time travel last year we tried to ease everybody into it and we tried to do the same thing here. … Now we’re really going to pick up with [episode] five and with six and seven – the Earth-Two storyline. There will be doppelgangers and doubles.”

The Flash
airs Tuesdays at 8 p.m. PT/ET on The CW.

Danielle Panabaker recently dropped by the ET offices to dish on all things The Flash. Press play to watch the interview!