Well, that was certainly one way to end an episode.
The entire world is talking about the shocking conclusion to The Power of the Doctor, which saw Jodie Whittaker's Thirteenth Doctor regenerate into her old Tenth Doctor form, as played by David Tennant.
It was a jaw-dropping conclusion (and with no explanation yet as to how this happened, fans are chomping at the bit to find out what happens next), but it wasn't the first time that the show has left viewers surprised.
Since it first hit the air in 1963, Doctor Who has pulled out some of the greatest episode endings in British TV history.
The size and scope of a show about the entirety of time and space means that literally anything can happen to the Doctor and their companions, which has led to some truly memorable cliffhangers over the years.
Drastic decisions, mind-blowing plot twists, events changing totally out of leftfield - it's all happened in Doctor Who, so we've rounded up ten endings that left viewers wondering what the hell they just witnessed.
Usually in a good way, but not always.
10. The Time Of Angels
The Weeping Angels were still new and exciting when this episode rolled around.
Before their creator Steven Moffatt diluted their effectiveness, the Angels were a force to be reckoned with, and had the Eleventh Doctor and his friends cornered underground with seemingly nowhere to run.
After some back-and-forth with the strangely charismatic Angel Bob, the Doctor announces that his enemies made a huge mistake by placing him in a trap. He then grabs a pistol and shoots the gravity globe that had been illuminating the cave.
It's not the greatest cliffhanger in the world, so why does this episode appear on this list? Well... because the Doctor used a gun.
Fans had been repeatedly told that the Doctor hated all weapons - especially guns - always opting for the peaceful solution to any conflict. To see Matt Smith's incarnation of the character wield one so freely (and so early in his lifespan) was more than a little jarring.
While he didn't fire it at a living creature, the juxtaposition of the universe's peacekeeper holding a firearm was enough to leave fans going - all together now - "WHAT?!"