Warning: This post contains spoilers for Star Wars: The Rise of Skywalker.

When Carrie Fisher passed away in December 2016, the current forces behind the Star Wars franchise made it clear that the actress wouldn’t be replaced by a new performer — Meryl Streep, for example — or a digital avatar for the final episode in the sequel trilogy, The Rise of Skywalker. Instead, director J.J. Abrams used eight-minutes of extra material from his 2015 film, The Force Awakens, as well as Rian Johnson’s 2017 follow-up, The Last Jedi, to craft a send-off to Fisher’s signature alter ego, General Leia Organa. That said, there is one crucial sequence in the film where Leia is (briefly) portrayed by another actress. Midway through the movie, we jump back in time to the post-Return of the Jedi era, when Luke Skywalker (Mark Hamill) trains his Force-sensitive sister in the ways of the Jedi.

Speaking with Yahoo Entertainment, ILM Visual Effects Supervisor Patrick Tubach says that Hamill played the “young” Luke in that sequence, and had his youthful appearance restored thanks to the magic of de-aging technology. But they also needed an actress to perform Leia’s role, someone whose face would be digitally replaced by a younger version of Fisher in the finished film. When the time came to shoot that scene, Abrams decided to keep the part in the family by asking Fisher’s daughter, Billie Lourd — who also plays Resistance lieutenant Kaydel Ko Connix in the sequel trilogy — to take on the mantle of Leia. “Billie was playing her mother,” Tubach reveals, confirming rumors that first surfaced online this past spring. “It was a poignant thing, and something that nobody took lightly — that she was willing to stand in for her mom.”

Lourd’s performance as Leia lasts mere seconds in terms of screentime, but Tubach and the rest of Rise of Skywalker’s visual effects team understood the drama of the moment. “It was an emotional thing for everybody to see her in that position. It felt great for us, too. If you’re going to have someone play [Fisher’s] part, it’s great that it’s [Billie] because there are a lot of similarities between them that we were able to draw from. The real challenge was just making the Leia footage we had to work with fit in that scene.” (As far as where the footage of the young Leia comes from, Rise of Skywalker co-writer, Chris Terrio, recently told The Hollywood Reporter that the filmmakers used images from Return of the Jedi.)

The limitations of that archival footage also meant that the flashback scene had to be kept short and sweet. “What you see is what we developed,” says visual effects supervisor, Roger Guyett, shooting down speculation that there might be a longer version of Leia’s Jedi training. “The idea was to provide this great surprise where they take the helmets off, and you see Luke and Leia’s younger faces. We scoured outtakes from the original movies, and we took some pieces and then had to try and figure out the technical aspect of putting that shot together.” As to whether Leia’s likeness might ever be used again in a future Star Wars movie, Guyett suggests that’s up to the actress’s family, particularly Lourd. “The truth is that Carrie was a friend of J.J. and Billie is a friend of J.J. They talked a lot about that, and I think the heart of it is the utmost respect for Carrie and her memory and her performance.”

Respect for Fisher’s memory and performance were the guiding principals the VFX team used for all of Leia’s scenes in Rise of Skywalker. “When you see her in this movie, it's the live-action element of her face taken from outtakes of either The Force Awakens or The Last Jedi, and then building a digital Carrie around that face,” he explains. “She's wearing a new costume, she's got new hair, she's got new jewelry. We didn't want it to feel like we'd simply taken previous shots from previous movies just edited her in; we wanted her to be unique to this movie, and we wanted her to be integrated into the scenes. J.J.’s principal in pre-production was, ‘I want Princess Leia to be played by Carrie Fisher. How do we do this?’ That was the integrity that he wanted brought to it, so that he could really put his hand on his heart and say that Princess Leia was always played by Carrie Fisher.” Well… Carrie Fisher and Billie Lourd.