It was Doctor Who's best-kept secret... until it wasn't.
John Simm reprising The Master was intended to be revealed in a Coming Soon trailer for the 10th series airing next Saturday, April 15, after the transmission of opening episode 'The Pilot'.
But the news leaked and was later confirmed by the BBC itself: "I can confirm that it's true," Simm said. "Thanks to the power of time travel, I'm back."
Head writer and executive producer Steven Moffat lamented that "nothing stays secret for long on Doctor Who," before adding: "But you'll have to wait a little bit longer to see exactly what The Master is up to and how he makes his return to face the Doctor."
It's a good point. Even with the news of Simm's reappearance out there, one big question still presents itself: how the hell are they going to pull it off?
Since Simm's last appearance on the show – in David Tennant's own swansong, 2010's 'The End of Time, Part Two' – the Master has of course been reinvented, regenerating into female form as Missy (Michelle Gomez).
Related: "I am The Master!": Who is Doctor Who's greatest nemesis?
Presumably, then, the Simm-Master will be plucked out of an earlier point in his time-stream to face off with Peter Capaldi's Doctor – and, indeed, share some screen-time with his successor (That's certainly how Doctor Who has always reintroduced previous Doctors, going all the way back to 1972's 'The Three Doctors').
The problem is, there aren't many suitable gaps in Simm-Master's past from which to pluck him.
Fans with long memories will remember that we saw Derek Jacobi's version of the Doctor's arch-rival regenerate into Simm's in the 2007 episode 'Utopia' – with the new Master then heading to Earth, where he assumed the alias Harold Saxon and was elected Prime Minister of Great Britain.
It's possible that there's a little give in The Master's timeline here – but the series always seemed to imply that he'd travelled directly from the planet of Malcassairo to Earth, with no room for an encounter with a future Doctor inbetween.
The Master's ploy, to pose as Saxon until he could unleash the alien Toclafane on Earth and rule over our devastated planet, ended with his apparent death. The Simm-Master did indeed lie dormant until resurrected by a cult of followers in 2009's 'The End of Time, Part One'.
After one more skirmish with the tenth Doctor, The Master turned on the Time Lords, who had been subtly manipulating him since childhood. In an act of self-sacrifice, he sent Rassilon (Timothy Dalton) and his hordes back into the Last Great Time War – a devastating conflict with the Daleks – sealing himself away with them.
All of this happened sequentially, with no obvious gaps in The Master's timeline. But it's what happened to him next that provides story potential for Simm's back.
When the character resurfaced, he had become a she, with the mysterious Missy revealing herself as the former Master in 2014 episode 'Dark Water' – but the exact circumstances of how Simm's Master had met his end were left ambiguous.
It was later implied that the Doctor had inadvertently "saved" Missy / The Master when he'd travelled back into the events of the Time War, transporting his home planet into a pocket universe, to save it from the Daleks.
But there's clearly a whole lot more to explore here – the transition from Simm to Gomez, and how Missy subsequently escaped Gallifrey. We've been promised that we'll see Missy and the old Master "face to face", but is that simply a clever-clever way of telling us we'll see one regenerate into the other?
We already know that Steven Moffat, as a fan himself, likes to fill these sort of gaps in the Doctor Who canon. For the longest time, we had no idea how Paul McGann's eighth Doctor gave way to Christopher Eccleston's ninth, until Moffat revealed what happened (shunting John Hurt's War Doctor in there between the two).
The lost period between the Master's sacrifice and Missy's arrival would seem to be the natural point to revisit Simm's incarnation – and might mean another return trip to Gallifrey.
One thing we know for certain – with Missy confirmed for Doctor Who's series 10 finale, that's when we can expect the old Master to resurface too, along with the original Mondasian Cybermen.
Quite the send-off for Peter Capaldi, ahead of his Christmas exit...
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