【Michael Maien】

Doctor Whohas brought the title character's regenerations together a few times before,Michael Maien most recently Matt Smith and David Tennant in the fan favorite 50th anniversary special "Day of the Doctor."

Now, for the first time, the show will offer two regenerations of the Doctor's psychotic Time Lord enemy -- the Master -- on screen at the same time.

Showrunner Steven Moffat confirmed Thursday that John Simm, who last played the Master at the end of Tennant's run in 2010, will return in the upcoming Season 10. Simm will be appearing "face to face" with Michelle Gomez, who plays the Master's current incarnation, Missy.

"It's not often you get to see a solo personality clash," Moffat said in a statement, adding that he'd hoped to keep their meeting a secret for longer. "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."

Whatever happens between Master and Missy, it's sure to be absolute insanity. In classic old-school Doctor Who, the Master was a classic old-school villain, right down to the evil beard and booming laugh.

But Simm and Gomez both brought their own brilliantly twisted 21st century take on the Master -- Simm playing the character as a petulant platinum blonde raver kid in a hoodie, while Gomez's version is a bug-eyed mad Mary Poppins who would just as soon kiss you as kill you.

It has never been explained how or why the Master regenerated into Missy -- or even how he escaped the funeral pyre on which John Simm's character was placed. But it has since been firmly established that Time Lords can change gender when they regenerate.

And the Master does have a habit of escaping what looked like certain annihilation. "Death is what other people do," Missy told the Doctor's companion Clara, who was shocked to find her alive at the beginning of Season 9.

One thing's for sure. Given the Master's general level of self-regard, and the fact that both Simm and Gomez have enjoyed on-screen makeout sessions, it's a virtual certainty that if the two versions of the Master meet, there's going to be some strong sexual chemistry between them.

And that will give fan fiction writers -- and students of Doctor Who's relationship to sexuality and gender -- many years of material.

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