Doctor Who fans were stunned by a surprise regeneration that saw David Tennant return to the Time Lord role in the BBC centenary special episode.
Sunday night's The Power of the Doctor was Jodie Whittaker's last appearance in the lead role and she had been expected to regenerate into Ncuti Gatwa, who will pick up the baton as what fans now know will be the Fifteenth Doctor.
Read more: Every Doctor's regeneration so far
But viewers were thrilled to see former star Tennant, who played the Tenth Doctor, make a surprise return to the sci-fi show's special marking the BBC's 100th anniversary and becoming the Fourteenth Doctor.
Tennant's Doctor made reference to his first appearance where he remarked on having new teeth by saying: "I know these teeth."
He then looked down at his outfit and said in confusion: "What?"
Fans couldn't believe that one of their favourite stars had returned, with Star Wars actor John Boyega tweeting: "David Tennant- The best doctor ever !!!"
Another fan wrote: "So DAVID TENNANT is the current Doctor! Just let that sink in for a moment…"
Someone else commented: "DAVID TENNANT IS BACK AS THE DOCTOR! I am lost for words currently."
Another person tweeted: "david tennant back on doctor who feels surreal"
Many viewers made the same joke about Tennant returning to his old job on the same evening that former Prime Minister Boris Johnson announced he would not try to pick up his old role.
One viewer tweeted: "David Tennant has returned to Doctor Who and Boris Johnson has pulled out of the leadership contest. This might just be the best 10 minutes of my life."
Someone else wrote: "Really happy the person getting their old job back tonight was David Tennant and not Boris Johnson."
This won't be the last that viewers will see of Tennant as the Doctor, as three new specials where he will be reunited with co-star Catherine Tate were announced for the show's 60th anniversary in 2023.
Gatwa will then take over as lead, making his series debut over the 2023 festive period - with a clip of his regeneration showing him asking: "Will someone tell me what the hell is going on here?"
Russel T Davies, who is returning as showrunner, said: “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!”
Watch: Jodie Whittaker regenerates back into David Tennant on Doctor Who