While some of these minor references have been developed inDoctor Whospin-offsover the years, several still remain a mystery.
Peris fate remains one ofDoctor Whos most controversial changes, opening the door for her return in the future.
This is a period of his life that remains sadly unexplored in the show.
It was briefly explored in a short story titled Picnic at Asgard, but never on-screen.
Its one ofDoctor Whos most interesting concepts, but the series has shied away from portraying the actual expedition.
This important piece of lore has not yet been mentioned in the show.
That means theres over two decades of stories between the Doctor and River on Darillium that havent been explored.
