As I said on Tumblr, until canon proves the contrary, I will go with "Hup moved on from Deet, fell for Ydra, married her, found Kira, raised her with her and taught her everything he knew about Gelflings to her because she was the last thing remaining from his dead friends he couldn't have saved and he saw her in them every day she laughed and this helped soothe a little his guilt for having been a mediocre paladin unable to fight the Garthim"
More details : https://ben-the-hyena.tumblr.com/post/190087336037/fuck-here-comes-the-feel-train

The Dark Crystal, Hup and Kira © the Jim Henson Company
Drawing, idea and theories © me