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It's the end ... but Watch Money Heist Onlinethe moment has been prepared for.

Peter Capaldi's run as the Doctor will finish after this year's Christmas episode of Doctor Who. Capaldi passes the reins to Jodie Whittaker, the first woman cast in the role. Now, just days before the special airs, the folks at the BBC are helping fans get ready for the transition with a Facebook lens that gives a taste of what it's like for the titular Time Lord to regenerate.

Regeneration, of course, is what happens when the Doctor grows too old or is mortally wounded, triggering a process in which his (or her) entire body transmogrifies into a completely different person. Practically, it means the show has a built-in reboot mechanism, letting the BBC keep the franchise going as long as it wants, bringing in new casts and production crews on a regular basis.

On the show, a regeneration usually kicks off with the Doctor's skin starting to glow, getting brighter and brighter beneath his clothes until he's totally engulfed in light. The light slowly fades, revealing a totally new person (or the same one, in at least one case).

That's pretty much what the Facebook lens does to you: First it shows the Doctor's TARDIS appearing behind you. An eyebrow-raise kicks off the regeneration light. Nodding your head makes it brighter, then it suddenly fades, revealing ... well, you. Likely unchanged.

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Still, fun stuff. You can try it for yourself by launching the Facebook camera in the top-left corner of the app, tapping the "magic wand" icon, and looking for the Doctor Whologo among the goofy holiday icons and lenses for Star Wars, Game of Thrones, Justice League, and others. Or just click here.

Any developer can create a lens with the Facebook AR Studio and submit it for Facebook's approval, though some businesses may pay for targeting. The BBC says the regeneration lens is available worldwide.

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