The Doctor was reunited with some familiar faces from the United Nations Intelligence Taskforce (UNIT) in tonight's series finale, and not all of them made it to the end. But one surprise survivor owes her life to a man whose face we never saw (except in a portrait earlier in the episode) but whose identity will have been clear to many Doctor Who fans.

The Doctor's former friend and UNIT founder Brigadier Sir Alistair Gordon Lethbridge-Stewart, aka the Brigadier, was among those raised from the dead and transformed into a Cyberman by the Doctor’s arch-enemy Missy  just in time to save his own daughter, UNIT’s Head of Scientific Research Kate Stewart, from certain death.

We didn’t get to witness the miraculous rescue that apparently involved him plucking her out of the sky after she was sucked from a plane thousands of feet up (and it’s hard to imagine exactly how a stainless steel Cyberman would catch someone falling at that rate without killing them) but it was the Doctor who deduced “The Cyberman must have caught her”. And when Clara informed him “Doctor, she’s talking about her dad,” the penny dropped.

“Of course… the Earth’s darkest hour, and mine, where else would you be?” asked the Doctor, before giving the Brigadier the salute he’d always wanted from his Gllifreyan friend. I like to think I wasn’t the only one who felt a shiver down their spine at that point…

Just one question remains – will we see the CyberBrig again? He was last spotted blasting off into the stratosphere, but unlike the rest of Missy's metal army he didn't blow himself up.

If Clara really is leaving, could the Doctor's next companion be made of metal...?