Ever since it was announced that an episode of the new series of Doctor Who would be filming on Lanzarote, fans have been speculating that it could mean the return of the Master.
The Spanish island was last used as a location for the series in 1984 episode Planet of Fire, when Peter Davison's fifth Doctor faced his Time Lord foe. And showrunner Steven Moffat has admitted that the Doctor is indeed "returning to the scene of an old adventure".
But what if Planet of Fire is not the "old adventure" Moffat's talking about? And what if Peter Capaldi's new Doctor is going to meet another familiar face instead – his own...
The wildly speculative argument goes as follows: the new episode is set against the backdrop of the volcanic island of Lanzarote. The last time Doctor Who featured a volcano was 2008 episode The Fires of Pompeii. And the major guest-star in that episode was... Peter Capaldi.
Capaldi played Roman merchant Lobus Caecilius, who was saved from the eruption of Vesuvius by David Tennant's tenth Doctor. He also popped up in Torchwood as Home Office permanent secretary John Frobisher. So since his casting as the Doctor, viewers have been wondering if (and how) the presence of two men with the same face as the Time Lord would be explained.
Well according to Steven Moffat there is a solution, cooked up by then Who head honcho Russell T Davies and passed on later to his successor.
"We are aware that Peter Capaldi’s played a part in Doctor Who before and we’re not going to ignore the fact," Moffat told Nerd3 last year. "I’ll let you in on this. I remember Russell told me he had a big old plan as to why there were two Peter Capaldis in the Who universe, one in Pompeii and one in Torchwood.
"When I cast Peter, [Russell] got in touch to say how pleased he was, I said 'Okay, what was your theory and does it still work?' and he said 'Yes it does, here it is'... It’s actually quite neat".
Whether Moffat will draw on Davies's idea this early on in Capaldi's tenure, who can say. But if you're watching series eight of Doctor Who this autumn and lava starts spewing into the air, you might want to prepare yourself for a rather unusual face off...