The following contains spoilers from the first four episodes of "The Circle" Season 4.

"I'm actually a bit scared now — my heart's beating really fast," Mel B tells Emma Bunton upon entering "The Circle."

That's right, two of the Spice Girls are on the fourth season of "The Circle," Netflix's social experiment/reality competition in which contestants build online personas for bonding and backstabbing each other without meeting face to face.

"They were absolutely brilliant, and we loved having them," says executive producer Toni Ireland. "I'm thrilled that we've kept it secret for so long."

The pop superstars are on the social media-based series because of, well, social media: Bunton once noted on Instagram how much she enjoys the show. Thankfully, Mel B was also a fan, and the two alumnae of the 1990s girl group were game to go in together and play as a single persona.

"It's the perfect show for a celebrity to play with complete anonymity," says Ireland, who noted that the British edition recently included famed broadcaster Richard Madeley, and previously launched a one-off with an all-celebrity cast to raise money for charity.

Instead of having them compete to win like the rest of the contestants, Bunton and B went into "The Circle" for a four-day period with a specific mission: If they could remain in the game as an undetected "catfish," the prize money would be upped an extra $50,000.

"We're always looking for ways to elevate the format, to make it bigger and better for the viewers ... so we came up with this fun twist," says Ireland of the fourth season, filmed last fall in Salford, England. "Also, watching the dynamic of two people playing the game together is interesting because they might not always agree."

"From the moment they found out about what they had to do, you can see it: They were just all in," she adds.

The pair's persona is "Jared," a 28-year old male who works as a children's author.

"We need to think of what our books are called, and how many books have we written," Bunton stresses in the second episode. "I feel pretty nervous about making sure we know everything about Jared. We gotta write it all down, we just gotta be clever about it." (They eventually tell the other players that Jared writes books about animals and poop, because "The kids dig it!")

"Jared" immediately starts forming friendships with some contestants, and even starts flirting with another. Between strategic chats and fun challenges, viewers get to see the two Spice Girls in a relatively normal setting: stewing berries in their pajamas, tidying up the kitchen, playing card games and lounging alongside B's dog, Cookie.

"They really are living together while they're in there," says Ireland. "They weren't treated any differently than any of the other players. They're clearly brilliant friends."

Bunton and B are put in the hot seat beginning with the third episode, when all the players are gifted 1990s memorabilia, sing along to Spice Girls songs and share memories of the girl group.

They then announce virtually to the other players that they're playing the game, and everyone must guess which profile they're secretly behind. (Bunton and B try to fool the others by saying "Jared" isn't a Spice Girls fan, yet is still excited at the prospect of playing alongside his sister's favorite musicians.)

A round of Spice Girls trivia, quizzing players on the group's movie and Olympics ceremony performance, only makes the game murkier.

Without knowing the consequences of the twist, the players then vote on who they each think is the Spice Girls' persona; a majority of them have to be fooled in order for Emma and B to complete their mission. The season finale, hosted by Michelle Buteau, will be released May 25.

After that, "The Circle" is open to more celebrities in the future, says Ireland.

"If anyone is interested in playing the game and thinks they've got what it takes, then they can absolutely reach out to us," she says. "Though, the Spice Girls are icons — where can we even go from there?"