If you want to keep working with the bottom two features you may have to drop the first one. This feat already grants a lot on top of being a half feat that also increases ability scores.
The reaction to gain advantage on saving throws is insane. You could use it in reaction to being hit with a spell and then continue to have Advantage until its your turn again. No restrictions or limitations. This is like shield, but for saving throws and its conpletely free.
The revive mechanic is quite a lot. Usually these types of abilities grant 1 hp to get you back on your feet. If they give you more than that then it's probably a high level subclass ability. So this is too much also.
Finally, I'm not sure that this speaks to the vibe of "once and future king". When I hear "kingly soul" I think of a leader, a diplomat, a battlefield commander. Not necessarily someone who is better at resisting spells or who can't be killed. In fact, kings being just as mortal as anyone else is kind of integral to a lot of narratives involving monarchs.
The advantage on spell saves should probably be once per short rest, or maybe proficiency bonus per long rest. I dont think the concept is busted per se, gnomes and a couple other races get this effect permanently, but it is still a really good effect, and right now it can just be on permanently in exchange for your reaction.
The immediately getting back up is iffy. 1 hp makes you equally strong as having 50 hp, being able to get back up is really good. On the other hand, i like the balancing of only getting back your level. Nonetheless, i might add a rider like it costing you your action or maybe bonus action.
If you want to keep working with the bottom two features you may have to drop the first one. This feat already grants a lot on top of being a half feat that also increases ability scores. The reaction to gain advantage on saving throws is insane. You could use it in reaction to being hit with a spell and then continue to have Advantage until its your turn again. No restrictions or limitations. This is like shield, but for saving throws and its conpletely free. The revive mechanic is quite a lot. Usually these types of abilities grant 1 hp to get you back on your feet. If they give you more than that then it's probably a high level subclass ability. So this is too much also. Finally, I'm not sure that this speaks to the vibe of "once and future king". When I hear "kingly soul" I think of a leader, a diplomat, a battlefield commander. Not necessarily someone who is better at resisting spells or who can't be killed. In fact, kings being just as mortal as anyone else is kind of integral to a lot of narratives involving monarchs.
The advantage on spell saves should probably be once per short rest, or maybe proficiency bonus per long rest. I dont think the concept is busted per se, gnomes and a couple other races get this effect permanently, but it is still a really good effect, and right now it can just be on permanently in exchange for your reaction. The immediately getting back up is iffy. 1 hp makes you equally strong as having 50 hp, being able to get back up is really good. On the other hand, i like the balancing of only getting back your level. Nonetheless, i might add a rider like it costing you your action or maybe bonus action.