Having finished the Deltora Quest series yesterday (the first one, I'm midway through the second), I'm of the opinion Doom should have been Endon and Lief Jarred's son.
Nothing in the Belt of Deltora book says that Adin's heir is through his bloodline; Lief could be the heir by virtue of being the one who took the effort to find the gems and unite the tribes once more. And Jasmine of course didn't want to be the heir to begin with. (good way to escape "blood gives you the right to rule")
Meanwhile, amnesiac Doom being utterly bitter about Endon's stupidity and forming the Resistance against the Shadow Lord feels so poignant when he's Endon himself.
I don't buy the explanation about how when the Shadow Lord took over, there was so much confusion that no one noticed Jarred and Anna switching with Endon and Sharn. I refuse to believe that their neighbours would manage to brush off how the duo seem completely different now.
Sharn being Lief's mother does explain how she created an invisibility cloak, but just explain that some other way :p.
Although Lief's father being Jarred and dying after all he sacrificed for Endon's and Deltora's sake is sad, I find the thought of Endon!Doom helping Lief who's now the true ruler to be fun :p.
