We then see that shot of the three Doctors in the current Tardis that was released a while ago and what looks like the Tenth and Eleventh Doctors in a UNIT base with two Kate Stewarts. Twin sister? Similar looking colleague? Some kind of wibbly wobbly timey-wimey... stuff? Probably the second one to be honest.
While next to a stone building with the Eleventh Doctor (possibly in Elizabethan England) The Tenth Doctor asks "Why are we all together? Why are we all here?". Because it's the 50th Anniversary, Doctor. Didn't you hear? This question's probably directed at the Hurt Doctor since he'd be the person most likely to have an answer. After that, Rose walks towards something while looking up on a plain of what looks like snow or incredibly white sand, and Clara cries.
The sonic rivalry continues with the Tenth Doctor's looking like the poor relation of the two, and the Eleventh Doctor says he almost remembers something as he throws his fez into a vortex. No! Not the fez!
And then, the absolute proof that this will be a love letter to all fifty years of Doctor Who: the Tenth Doctor looks around the Eleventh Doctor's Tardis and utters that now immortal line "Oh, you've redecorated. I don't like it", much to the Eleventh Doctor's annoyance. A variation of this line was first used by the Second Doctor in The Three Doctors forty years ago and has cropped up several times since then, almost becoming a staple of Multi-Doctor stories.