Doctor Who's BBC centenary special delivered quite the twist as Jodie Whittaker's Thirteenth Doctor regenerated into none other than David Tennant.

But what does it mean for the Fourteenth Doctor, Donna Noble and new Who star Ncuti Gatwa? To partially quote Gatwa's Doctor, here's everything we know about "what the hell is going on here".

"How? What? Why?" Showrunner Russell T Davies has said that fans will have a year to speculate about what's happening before "all hell lets loose" in three special episodes marking Doctor Who's 60th anniversary.

"If you thought the appearance of David Tennant was a shock, we’ve got plenty more surprises on the way!" he adds.

Read more below.