'The Great' star Elle Fanning says Gillian Anderson signed on to play Joanna after reading the character's ill-fated sex scene

• Gillian Anderson guest stars as Joanna, Catherine's mother, on season two of "The Great."
• She wanted the part after reading Joanna's sex scene in the script, Elle Fanning told Insider.

Warning: This article contains spoilers for season two of "The Great."

After Gillian Anderson found out that Joanna dies while having illicit sex with her son-in-law on season two of "The Great," the 53-year-old actress was sold, according to her costar Elle Fanning.

"I heard that Gillian read that scene," Fanning told Insider, continuing, "So she falls out and dies in that way, and gets fucked out the window."

The actress said: "Basically, Gillian was like, 'That's why I want to do this.'"

On season two, Joanna Elisabeth of Holstein-Gottorp visits Russian court to get to the bottom of a rumor circulating Europe that her daughter, Catherine (Fanning), staged a coup d'état to overthrow her husband, Peter (Nicholas Hoult).

If it were up to the tightly-wound German matriarch, her daughter would be an obedient royal wife, not a ruler.

Disappointed to learn that Catherine does, in fact, hold complete control over Russia, Joanna acts out against the empress' interests with covert attempts to seduce her son-in-law in episodes seven and eight.

Peter rejects Joanna's incessant come-ons, but she proves relentless. Ultimately, he acquiesces.

Sighing and closing his eyes, Peter mutters "fine" and has sex with his wife's mother. In the heat of the moment, he hoists Joanna up against a large window, and she plummets directly through it to her death.

Both Fanning and Hoult are executive producers in addition to leads on the show, which openly veers on the side of fantastical despite following a loose framework of real historical figures and events.

Provided that the real Princess Joanna didn't die in Russia (nor did she have sex with Peter), creator Tony McNamara's plans for the character came from left field. The plotline was hard to digest, even for those that had already been through an entire season of the campy, violent, and sexually explicit antics embedded in each episode of "The Great."

"I hit the cement floor. I couldn't believe it. I was so shocked I fell over," Hoult told Insider of the moment he read through the episode-eight script for the first time.

He added: "You hear rumors on set of what might happen, and people have been like, 'Have you read episode eight? Have you read nine?' Suddenly you read it and you're like, 'I can't believe Tony went there and that's what happens to your mom.'"

So, Hoult and Fanning began spitballing ideas for who would play ill-fated Joanna.

"When I heard about this, I was like, 'Who's going to be the mom? Because we knew that his character would have to do this," Fanning explained.

The 23-year-old actress said she raised Pamela Anderson's name as a potential option, smiling at Hoult as she recounted the story. She also joked that her costar pitched actresses from Jennifer Lopez to Halle Berry to portray Joanna before Anderson secured the role.

"[I was] thrilled with Gillian Anderson," Hoult assured.

Season two of "The Great" is currently available to stream on Hulu.