One of the more unique and most heart-breaking elements of Doctor Who is that every incarnation of the Doctor eventually regenerates. This is the process in which the Doctor changes forms from one life to the next with the help of Time Lord energy. It’s usually a bittersweet transition, with audiences being filled with incredible sadness as they mourn the previous Doctor and immense joy as they celebrate getting to know the new one.

The latest episode of Doctor Who had the 15th Doctor, played by Ncuti Gatwa, regenerate into the next incarnation during the end of his two-season tenure as the iconic character. Fans across the globe were shocked to see him regenerate into none other than Billie Piper.

Billie Piper has already appeared in the popular TV series. She played the character Rose Tyler, the Doctor’s first companion when the show was rebooted back in 2005. Now, the Doctor is using her face as their next regeneration, which is surprising and a little bizarre. It makes one wonder why that is.

This isn’t the first time the Doctor has regenerated into a familiar face. Peter Capaldi was originally in the 2008 episode “Fires of Pompeii,” in which he portrays the sculptor Caecilius. He later became the 12th Doctor in 2014. In the show, the characters wondered why he now had that face, and it was seemingly to remind him of the importance of saving someone in every situation and the importance of life. That was the core theme of Capaldi’s 2008 episode.

So there must be a reason for using the face of Rose Tyler, right? She was a much more major character than Capaldi’s Caecilius, so having the Doctor regenerate into her is no coincidence. What could the significance be?

The Doctor’s regeneration typically represents character development of sorts. Yes, it’s when an actor is leaving the show, but story-wise, it’s when the Doctor reaches a full arc or when they come to some emotional realization. When the Doctor regenerated from Christopher Eccleston to David Tennant, it was in a moment when he started to like himself a bit more and was finally able to let go of some of his guilt. When he regenerated from Capaldi to Jodie Whittaker, it was when he learned to be more caring to those around him and see the world with a brighter outlook.

There’s got to be a big reason for the Doctor to regenerate into the face of such a beloved companion. My big theory is that it all has to do with love. During Jodie Whittaker’s run as the 13th Doctor, she clearly had romantic feelings for her companion, Yaz. However, she never got herself to admit that she loved her to her face.

Right before Ncuti Gatwa’s 15th Doctor sacrificed himself to change the timeline just enough to ensure a little girl named Poppy existed, which led to his regeneration, he got the chance to have a conversation with his past self in the form of Whittaker’s Doctor. During that scene, they exchanged a couple of lines about her feelings for Yaz and how the Doctor has always had trouble telling people that they love them.

There was one big moment in Doctor Who when the Doctor did say “I love you,” after taking a while and even missing an opportunity to do so. That was when he said it to Rose Tyler.

Whether it be romantic love, platonic love, familial, or any other kind of love, it’s not something the Doctor has liked to admit out loud despite being full of love for those around them. With Rose being the one he’s admitted having love for, this face is a good one for a more open and loving version of the Doctor.

Because she now has this face, for however long that may be, it might be safe to assume that her version of the Doctor will be more open about her love for others. Love is a powerful motivator for doing what the Doctor does best, which is protecting people in need.

It’ll be intriguing to see how Piper portrays the iconic TV character going forward.

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