Warning! Spoilers for the Doctor Who season 15 finale!The regeneration of the Fifteenth Doctor, Ncuti Gatwa, into fan-favorite, Billie Piper. Whether Piper will be portraying the sixteenth incarnation of the Doctor is not yet confirmed. However, Piper’s surprising appearance wasn’t the only one that fans were excited to see. Jodie Whitaker also had a cameo as the Thirteenth Doctor, and viewers caught a glimpse of Jon Pertwee as the Third Doctor.

“The Reality War” continues where episode 7, “Wish World,” left off: with the Fifteenth Doctor seemingly falling to his death into the Underverse. He is rescued by none other than Anita, the hotel clerk from the 2024 Holiday Special, “Joy to the World.” Anita now works for the Time Hotel, and she explains to the Doctor that she has been looking for him for a long time by peeking into different doors from his past. One of the doors shows Matt Smith as the Eleventh Doctor, and seasoned fans of the series should recognize this moment in the Doctor’s timeline.

Where Matt Smith's Cameo In Doctor Who Season 15 Comes From

The Scene Is From Season 6, Episode 13 "The Wedding Of River Song"

When Anita opens the door to the Doctor’s past, she witnesses the Eleventh Doctor playing a game of chess while wearing a Stetson cowboy hat. The scene comes from season 6, episode 13 “The Wedding of River Song,” in which the Doctor knows that his death is imminent, and that the Silence is behind it. During the scene, the Doctor plays chess against one of the minions of the Silence - but it isn’t just any normal chess game, as the opponent's life is at stake. The Doctor agrees to lose the game in exchange for information about the Silence.

Since “The Wedding of River Song” is one of the most important and beloved episodes in the Doctor Who canon, it’s no wonder that showrunner Russell T Davies chose this particular Eleventh Doctor scene. There may also be a greater significance to using this River Song-centered episode: the connection between the Fifteenth Doctor and Belinda’s daughter, Poppy. Both Poppy and River were children of the Doctor’s companions, and both have pivotal roles in the Whoniverse.

Doctor Who's Past Doctor Cameos Make Anita A More Important Character

Anita Might Have An Important Role In Future Doctor Who Episodes

It’s a known trait of the Doctor to pop in and out of people’s lives and leave a lasting impact, and that was also true for Anita. In “Joy to the World,” the Fifteenth Doctor visits the Time Hotel, where every door is a room that leads to a specific time and place. When the Doctor ends up trapped in 2024, he has to wait a year on Earth before he can return to the Time Hotel. He takes a job at the Sandringham Hotel in London, where he meets the manager, Anita.

When it's time for the Doctor to leave, Anita is heartbroken to say goodbye to her friend. Yet in one of the final scenes in “Joy To The World,” a woman from the Time Hotel appears and offers Anita a job, as she was “highly recommended” by the Doctor. Her reappearance in “The Reality War” is not only a callback to the holiday special, it also highlights Anita’s importance to the Doctor Who canon.

If Anita is able to open doors to the Doctor’s past regenerations, it means that she may continue to have an even larger role in the series. New storylines might have a need for the Doctor to revisit his timeline, or there might even be added lore in which Anita has already affected the Time Lord's past. Of course, all of this hinges on whether Doctor Who gets renewed for season 16.