After it was announced that David Tennant and Catherine Tate would be returning to Doctor Who to celebrate the show's 60th Anniversary next year, fans naturally assumed that Tennant would be reprising his role of the Tenth Doctor, which he played from 2005 to 2010.

Tennant is a fan-favorite Doctor and, after his return to the role for the show's 50th Anniversary special, "The Day of the Doctor" (2013), fans are excited to see him once again.

However, after a vague press release from the BBC, cryptic Instagram posts by returning showrunner Russell T. Davies and the unveiling of set photos showing Tennant and Tate back in action, fans are starting to question whether the Tenth Doctor really is back. 

And if he isn't, then who is this mysterious version of the Doctor, and why does he look like David Tennant?

With the Tenth Doctor being one of the most popular versions of the character, it was almost certain that Tennant would return for the 60th Anniversary, especially considering it's written by the man who cast him, Russell T. Davies.

As soon as Tennant was announced to be returning, the rumors began circulating, with many fans wondering what it meant for Ncuti Gatwa, who had been announced to play the new Doctor a week before.

Will fans see Gatwa's Time Lord at the end of Jodie Whittaker's last story, then spend a few episodes with the Tenth Doctor again?

But how could both Tennant and Tate return, with the Doctor and Donna Noble having been separated and Donna having no memory of her adventures with him? Usually, this would be easily explained away in typical Doctor Who fashion, with the adventure taking place during the characters' past, sometime during the events of Series 4 (2008). However, this may not necessarily be the case.