With all the excitement in this week’s episode of Doctor Who (creepy Cybermen! John Simm’s return! Regeneration! The apparent death of Pearl Mackie’s Bill!) you’d be forgiven for not noticing some subtle hints about what’s to come in the final days of Peter Capaldi’s Twelfth Doctor.

And we reckon this hint could suggest what awaits the Doctor in the Christmas special – because the episode’s spine-tingling opening scene (which appears to see the Doctor start to regenerate at a future point in the series) appears to call back to a classic story from the original series.

We’re talking specifically here about famed 1966 serial The Tenth Planet, which saw the Doctor (William Hartnell) and his companions travel to the South Pole only to grapple with the original Mondasian Cybermen as they attempted to take over the human race.

Of course, you’ll have already noted a couple of connections between that story and this week’s episode World Enough and Time – they both explore the early days of the Mondasian Cybermen who would evolve into one of the Doctor’s deadliest foes throughout the series, and both also deal with the Doctor’s regeneration.

In fact, the Tenth Planet featured the very first changeover between incarnations of the Doctor as ailing actor Hartnell handed over to new face Patrick Troughton in the serial’s final moments (below), while World Enough and Time appears to show us the moment Capaldi’s Doctor begins the same process.

But after viewing tonight’s episode it seems like the connections don’t stop there. The choice of locale for Capaldi’s regeneration – the aforementioned icy wasteland – seems like an intentional callback to the Tenth Planet’s South Pole setting, while static black-and-white shots of the Doctor, Missy and Nardole watched by Bill on an old TV from her faster timestream seem to recall the aesthetics of Hartnell’s older stories.

Now, these observations wouldn’t be worth making were it not for the fact that it’s long been rumoured that Hartnell’s incarnation of the Doctor is returning for star Peter Capaldi’s final episode this Christmas, with David Bradley (who played the actor and the First Doctor in 2013 making-of biopic Adventures in Space and Time) apparently set to fill in for the deceased Hartnell as the Time Lord’s first incarnation.

With that in mind these new details take on a larger importance, with the icy planet suggesting either the Twelfth Doctor could run into his earlier self or simply providing a fun visual clue for fans about where the story is heading – a final farewell for both the First and latest Doctors.

Doctor Who series 10 concludes on BBC1 on Saturday 1st July