A host of characters from previous series of Doctor Who will return for an episode to mark the BBC’s centenary.
The Master, the Daleks and the Cybermen will feature later this year, as will two former companions of the Doctor, who will reprise their roles for the first time since leaving the show.
Janet Fielding, who played Tegan Jovanka between 1981 and 1984 will return, as will Sophie Aldred, who appeared as Ace alongside Sylvester McCoy’s Doctor from 1987 to 1989.
It will also be the final outing of Jodie Whittaker as the Doctor, after her departure was announced last year.
She made her first appearance as the 13th Doctor in 2017. Her successor has not been announced, but the name is expected to be confirmed in the next few weeks.
Sacha Dhawan will reprise his role as The Master for the episode, after playing the doctor’s arch-enemy in series 12 in 2020.
The comebacks were revealed in a trailer broadcast after the show’s special on Easter Sunday.
Fielding said: “In some ways it was a very different experience to what it was like when I finished recording in 1983, but in many ways it was very similar. It was so lovely to be a working member of the Doctor Who family again.”
Aldred said: “It’s been quite a challenge to have such a big secret to keep, even from my family, and I couldn’t be more thrilled and excited to have been asked back.
“I hope everyone enjoys it as much as I adored being part of the Tardis team again.”
Alongside Whittaker, showrunner Chris Chibnall will also be departing. He will be replaced by Russell T Davies, who was behind the high-profile return of the show in 2005, after 16 years away from TV screens.
Chibnall said: “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.
“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 13th Doctor.”