Doctor Who: Why Each Doctor Was Forced To Regenerate

Even though he got a little angry and arrogant towards the end, the Tenth Doctor's regeneration is ultimately a selfless, heroic moment.

After staring down the double-threat of Rassilon and the Master, the Tenth Doctor thinks he's won... but not so fast! That pesky 'four knocks' prophecy returns to haunt him once again, only this time, it's not a prophecy: it's a reality.

Frustratingly, Wilf has got himself trapped inside a booth that's about to be flooded with radiation, so he knocks on the glass door four times, and the Doctor's relieved expression quickly turns sour. The only way to save Wilf is for the Doctor to soak up all that radiation himself, damaging his body to the point of regeneration.

After doing this - and knowing that he's about to change - Ten heads off on a quick farewell tour, saying goodbye to all his old companions. After a final encounter with Rose Tyler, it's time for him to transform, and here, we're treated to a massive regenerative explosion that completely wrecks the interior of the TARDIS.

A sweeping camera move and a bright orange light later, and the Eleventh Doctor is born, yelling "GERONIMO!" as his time machine hurtles towards the Earth.