London, UK – Fans of the TV show Doctor Who are reeling and rejoicing at Jodie Whittaker's surprising regeneration into none other than David Tennant.

Whittaker’s tenure as the 13th Doctor and the first woman to lead the Sci-Fi show ended Sunday night in an episode titled The Power of the Doctor.

But instead of regenerating into her recently announced successor Ncuti Gatwa, she unexpectedly became none other than Scottish actor David Tennant, who previously played the Doctor between 2005 and 2010.

Per the BBC, returning critically acclaimed showrunner Russell T Davies said of the twist: "If you thought the appearance of David Tennant was a shock, we’ve got plenty more surprises on the way!"

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Tennant also appeared in the star-studded trailer for next year’s 60th-anniversary episodes, which was released after the show aired on Sunday night. This trailer confirmed he will be returning as the 14th incarnation of the Time Lord for a three episode special that will air in November 2023.

Tennant isn't the only actor returning for the special. The trailer also revealed that Catherine Tate will appear back in her role as the Doctor's former companion, Donna Noble.

The next incarnation Ncuti also made an appearance, as the upcoming 15th Doctor. At the end of the trailer, he demands: "Someone tell me what the hell is going on here?"

And as How I Met Your Mother's Patrick Neil Harris appeared as a villain with a top hat looking mighty pleased with himself, fans wondered the same.

After Whittaker's final episode as the Doctor aired and the trailer dropped, fans took to Twitter to gush over Tennant's return, with many simply writing, "OMG."

Others were sure this "could be the best regeneration to date."

Yet, some were a bit flabbergasted by the end of Whittaker's tenure and overwhelmed by the new reveals: "We're grieving Jodie here, hang on." Other Twitter users just wrote questions marks and "WHAT" in all caps.

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Regardless if fans are thrilled, in mourning, or itching to see how this twist plays out, they'll have to wait more than a year. Per Davies, "the path to Ncuti’s 15th Doctor is laden with mystery, horror, robots, puppets, danger and fun!"

"And how is it connected to the return of the wonderful Donna Noble?" he added. "How, what, why? We’re giving you a year to speculate, and then all hell lets loose!"

The 60 Anniversary episodes are set to air in November 2023, and will be followed by episodes with Ncuti as the 15th Doctor. Fans are on the edge of their seats.