http://tvtropes.org/pmwiki/pmwiki.php/Recap/DoctorWho2013CSTheTimeOfTheDoctor

It's time to say goodbye to Matt Smith.

— Clara Oswald "And now it's time for one last bow. Like all your other selves. Eleven's hour is over now. The clock is striking Twelve's ."

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The one where the Doctor gets naked.

The 2013 Doctor Who Christmas special. It features the final regular appearance of Matt Smith as the Eleventh Doctor, and the first regular appearance of Peter Capaldi as the Twelfth Doctor.

Orbiting a quiet backwater planet, the massed forces of the universes deadliest species gather, drawn to a mysterious message that echoes out to the stars. And amongst them — the Doctor. Rescuing Clara from a family Christmas dinner, the Time Lord and his friend must learn what this enigmatic signal means for his own fate and that of the universe.

This Christmas... Silence Will Fall.

Trailer 1. Trailer 2.

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"Kidneys!"