Farther Beneath the Planet of the Apes

When the apes and ponies initially interact there seems nothing amiss.  However, at some point the senior orangutan holds private council with Princess Celestia.   During this meeting in which they give evidence of a totally unexpected familiarity with each other they discuss the mutual dependencies of their respective societies and the deliberate obfuscations upon which they are based.  During this conversation we learn the following:

Both the ape and Equine societies exist in the same world.  The apes inhabit the 'outer universe on the outside of the planet while the equines inhabit the 'inner cosmos' on the inside.

Both societies have replaced the earlier human civilization that ruled the Earth and the leaders of both societies know this and keep this information from their respective populations because of the legacy of self destruction that the human society left behind and the threat of repeating the same mistakes poses to each.

The fact that each society is separated by such great distance allows for their co-existence.

At this point, the matter of the escort chosen for them is brought up.  Lyra's curiosity in ape and other hominid societies is mentioned as a possible threat to the current stability of their societies based upon mutual controlled ignorance.

At this point it is suggested that she be appointed as 'embassador' and allowed to accompany them back to the surface world.  The apes will deal with her there, their way..