Watch: 'Doctor Who' teases Jodie Whittaker's final adventure, return of classic 'Who' companions

Doctor Who has a long history of change, dating back to the departure of First Doctor William Hartnell in 1966. The changing of the guard known as Regeneration is built into the show's DNA at this point, but that doesn't make it any easier for fans to face down the loss of a beloved Time Lord. This fall, it's Jodie Whittaker's turn to say goodbye, and now we've got the first look at her final Doctor Who special. 

We've known since last July that 2022 would be Whittaker's final year as the Doctor, and we've since seen her wrap up her final series, "Flux," as well as two of three promised specials for this year. At the New Year we got "Eve of the Daleks," and over the Easter weekend we got "Legend of the Sea Devils." That leaves just one more story for the Thirteenth Doctor, and while we don't yet have a title for the special, we do know that it's coming sometime this fall, and in the ominous first teaser below, The Doctor is promised one thing: "This is the day you die."

Check out the teaser, and see if you can spot the two unexpected guest stars who emerge:

That's right, we've got a couple of additional companions riding along for Whittaker's final special, but we're not just talking about old friends from earlier in her run. Classic Doctor Who Companions Tegan (Janet Fielding) and Ace (Sophie Aldred), both of whom starred in the show back in the 1980s, are set to appear in the special, and they're diving right in to help The Doctor despite decades away from traveling in the TARDIS.

In Tegan's case, her tenure with the Time Lord ran through the end of Fourth Doctor Tom Baker's run and the beginning of Fifth Doctor Peter Davison's, wrapping up her run as a companion in 1984. Ace has the distinction of being among the final regular cast members of the classic Doctor Who run, joining Seventh Doctor Sylvester McCoy in 1987 and staying on until his run, and the run of the original show, ended in 1989. She didn't return alongside McCoy for the opening of the 1996 Doctor Who movie which saw the debut of the Eighth Doctor, so we really have no idea what Ace has been up to since she was last in the TARDIS. Now, we get to find out. 

But Tegan and Ace aren't the only big reveals coming in the finale of the Thirteenth Doctor's run. The final episode will also feature the return of The Master (Sacha Dhawan), as well as the arrival of other old friends and foes in what's set up to be a massive sendoff for Whittaker's Doctor. 

"Jodie’s final feature-length story contains a plethora of treats and surprises for audiences and fans, not least the return of two of the most beloved companions in the show’s history," showrunner Chris Chibnall told Radio Times. "They’ll be helping the Doctor fight on three fronts, against her deadliest enemies: the Master, Daleks and Cybermen, in one huge story!

"For the BBC’s Centenary, we’ll be celebrating the past, present and future of Doctor Who, in a fittingly thrilling, epic and emotional send-off for the Thirteenth Doctor."

There's still a lot we don't know about Whittaker's final special, which will also be Chibnall's final story as showrunner before he departs to make room for Doctor Who legend Russell T. Davies' return. We don't know how this Doctor will go out, who she'll leave behind, and who might replace her. What we do know is that, this fall, we should all prepare for the end of an era.

Jodie Whittaker's final Doctor Who special airs this fall on BBC America.

If you're looking for more sci-fi to check out in the meantime, you can find shows like Eureka, Warehouse 13, Brave New World, Resident Alien, Heroes, Sliders, Supernatural Academy and more on Peacock.