ok didnt see if anyone else caught this so im just going to put it out there.
i was rewatching season 5 episode the big bang and i noticed 2 things that relate to this episode.
1) when the Doctor takes the pandorica into the center of the exploding tardis he is taken into the NetherSphere ( River said that is what would happen to him, and that its the void between worlds). while he is in the NetherSphere he is like a ghost almost. he can see everything around him but no one can see him (altho amy can hear him)
2) at the very end of the episode where the Doctor, Amy and Rory are in the Tardis the doctor gets a phone call, the person (identified as “your majesty) needs the Doctors help with….the around him but no one can see him ( altho amy can hear him at the least)