Doctor Who fans have been left scratching their heads following the final moments of the latest episode of the beloved show, as Jodie Whitaker’s Thirteenth Doctor epically regenerated and transformed into...David Tennant’s Tenth Doctor. Who now also holds the title of Fourteenth Doctor. Speaking on BBC Radio 4’s Today show, Tennant has discussed his triumphant return to the iconic role of The Doctor, revealing that was mostly “worried it would be difficult to get in the groove again, but it has been straightforward.”

“We’ve managed to keep the essence of the show and the world now has a very exciting moment to look forward to. Doctor Who was a wonderful time in my life and it runs through me like a stick of rock so to be part of that show, go on that journey and return to it when I thought it was a memory has been an absolute present.”

The latest episode of Doctor Who saw Jodie Whitaker’s Doctor take on a multitude of villains, including The Master, the Cybermen and the Daleks. As Whitaker promised, the episode was "one for the Whovians. It's a huge treat if you're a proper fan. It's got all the iconic things that you associate with Doctor Who. It's massive. I love the dialogue Chris wrote for my regeneration. It captures my Doctor beautifully. It's simple, epic and beautiful. When I could see the crew was happy with that last shot, that's when my bottom lip started going. I was like, 'Well, they can't say they need another take now because I've f*cking lost it!'"

"I know these teeth," Tennant’s returning Doctor said once the show-stopping regeneration was complete, referring back to his first words as the character way back in 2005. For now, Doctor Who fans have no idea how or why David Tennant’s iteration of the Doctor has returned, but no doubt the internet will be full-to-the-brim with theories and speculation for months to come.

Related: David Tennant is Back as Doctor Who in New Set Photos

Returning Doctor Who Showrunner Russel T. Davies Has Teased Further Surprises

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BBC 

It seems that a comeback from both David Tennant and Catherine Tate, who will reprise the roles of The Doctor and Donna Noble, respectively, is far from the only surprise in store during the three 60th anniversary episodes of Doctor Who.

“If you thought the appearance of David Tennant was a shock, we’ve got plenty more surprises on the way. The path to Ncuti’s Fifteenth Doctor is laden with mystery, horror, robots, puppets, danger and fun. And how is it connected to the return of the wonderful Donna Noble? How, what, why? We’re giving you a year to speculate, and then all hell lets loose.”

While Tennant is expected to feature heavily in the upcoming episodes, which are not scheduled to air until November 2023, he will eventually make way for Sex Education star Ncuti Gatwa, who will take over as the Fifteenth Doctor. We have now had our first glimpse at Gatwa in the role, with the actor’s Doctor asking the question that we will no doubt all be asking for some time, “What the hell is going on?”