Doctor Whojust pulled off one of the most controversial moves in its six-decade run. Ncuti Gatwa regenerated into Billie Piper, the woman who played the Ninth Doctor’s companion Rose Tyler, and fans had very mixed feelings to say the least.

And Peter Davison, the man who portrayed the Fifth Doctor (and is also the father-in-law of David Tennant, the Tenth Doctor!) has mixed feelings too. He shared his thoughts with Starburst magazine recently. “I don’t know what Billie Piper is doing,” he said. “I have just read about it, and I don’t know what it’s about. It’s a completely mad idea.”

“I don’t think she is the Doctor,”he went on. And indeed, at the end of the regeneration episode Piper was notably not named in the credits as “The Doctor” – they simply said, “And introducing Billie Piper.” Fans have all sorts of theories about who this new regeneration could be. Perhaps she’s somehow Rose Tyler herself… or perhaps she’s the Bad Wolf, the being created when Rose looked into the Heart of the TARDIS all the way back in the Christopher Eccleston era.

“I think it’s kind of just a hand grenade thrown into the final episode to try and go ‘whoa, what’s this?’ And then it’s almost like ‘get out of that,'” Davison went on. “I love Billie Piper; I think she was the best companion there’s been. But that is partly because she was written in a different way from the other companions, it was almost like she was the center of the story. You were seeing the Doctor through her eyes. I thought she was a fantastic companion, but she’s got a great career, and she’s got options galore. I don’t know why she would voluntarily choose to go back to Cardiff [where the show is filmed] for a year.”

Billie Piper herself seemed more than happy to go back into the show that made her name, though. She said in a statement (via Radio Times) after her episode aired, “It’s no secret how much I love this show, and I have always said I would love to return to the Whoniverse as I have some of my best memories there, so to be given the opportunity to step back on that TARDIS one more time was just something I couldn’t refuse, but who, how, why and when, you’ll just have to wait and see.”

Doctor Who’s Future Is Up In The Air