Doctor Who fans have been thrown a surprise twist, with former Time Lord David Tennant reprising his role as the Doctor, after Jodie Whittaker's four-year stint as the first female Doctor comes to an end.
Warning: More spoilers ahead
The big reveal happened at the end of a new, 90-minute special, The Power of the Doctor, which is now available to stream on ABC iview.
Here's what you need to know about the feature-length episode, Tennant's surprise return and what comes next for the classic British sci-fi drama.
Surprise cameos and a big twist in The Power of the Doctor
The Power of the Doctor saw Whittaker's Doctor take on her deadliest enemies: the Daleks, the Cybermen and her arch-nemesis, the Master.
That episode also featured a host of familiar faces from the show's almost six-decade history.
Among them were the fifth, sixth, seventh and eighth Doctors, played by Peter Davison, Colin Baker, Sylvester McCoy and Paul McGann.
Former companions Ace (Sophie Aldred), Tegan (Australia's Janet Fielding) and Jo (Katy Manning) also appeared. As did 97-year-old William Russell, who played one of the companions of the first Doctor.
But it was latest Doctor's regeneration which received the most attention.
Instead of regenerating into her previously announced successor — Sex Education actor Ncuti Gatwa — Jodie Whittaker's Doctor returned as David Tennant, who played the Doctor between 2005 and 2010.
Here's the moment of the regeneration:
The BBC confirmed that Tennant has officially returned as the 14th Doctor.
He is reprising his role across three special episodes for the show's 60th anniversary, which are set to air in November 2023.
It was previously announced that Catherine Tate would also reprise her role as the Doctor's companion, Donna Noble, and that American actor Neil Patrick Harris would be joining the cast.
Tennant told BBC News:
"What a lovely, lovely thing to get to revisit something that was such a wonderful, happy, significant time in my life."
It was announced earlier this year that Tennant had been filming scenes for the show's 60th anniversary.
He told the BBC that he was left with "a whole mixture of emotions" when he left Doctor Who in 2010, including "sadness and regret".
"So, to be able to revisit that and to get another another shot, it was a total joy from start to finish," Tennant said.
"I thought it was something that I would certainly never be as involved in again … it's like being given the loveliest present.
"And I'm very, very excited. I'm thrilled and I hope people will enjoy the stories we've got to tell."
'More surprises' are coming before Ncuti Gatwa's Doctor
At the end of The Power of the Doctor, fans got their first glimpse of Gatwa — who briefly appeared in a teaser trailer (below) saying: "Someone tell me what the hell is going on here?"
Doctor Who Showrunner Russell T Davies says "more surprises" are on the way for fans before Gatwa takes over from Tennant as the 15th Doctor.
"The path to Ncuti [Gatwa]'s 15th Doctor is laden with mystery, horror, robots, puppets, danger and fun," he said, "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!"
The BBC says the first episode with Gatwa as the Doctor will take place "over the festive period in 2023".
He will be the first black actor to play the lead role in the series.
Whittaker said it was 'an absolute privilege' being the Doctor
Whittaker — who became the 13th Doctor in 2017 — said in a promotional video that she was "a different person" after her stint in the lead role.
"It has been an absolute privilege and a joy, full of laughter and tears, and everything you could have ever dreamed it to be," she said.
"Being able to play this gift of a role will, and has, changed my life for the better, and it's brilliant.
"All I ever wanted to be when I was a little kid, was I wanted to play pretend, and what a toy box I was given in playing this role.
"It's been amazing. I've absolutely loved it."
Whittaker told Radio Times that she hoped to return to the series one day.
"If I'm not asked back, I will be devastated," she said.
Doctor Who: The Power of the Doctor is available to stream on ABC iview, and airs on ABC TV Plus at 7.30pm AEDT on Monday, October 24.
