While JK Rownling's uncanny literary talent is already amazing by itself, what can make that even better is the sharp logic of her fans who come up with fan theories. While Harry Potter is known as The Boy Who Lived, this awesome new fan theory discovered on Tumblr claims that he can be The Boy Who Lived Forever.
Bustle reported on Tumblr user marauders4evr's fan theory which says that Fawkes might just have been Harry Potter's horcrux all the time. To drive this in, marauders4evr points out Harry's first encounter with Voldermort and the possibility of accidentally making a horcrux. This is when young Harry Potter stabbed a gigantic snake and when he did, a little piece of his sould merged with that of Fawkes', carrying him back to life. The theory gets even darker than that when it is remembered how fans went berserk after looking into what the prophecy said. "Either must die at the hand of the other for neither can live while the other survives," points out that for Voldermort to be gone, Harry should be immortal.
Inverse also said that when Harry killed the Basilisk way back in "Harry Potter and the Chamber of Secrets," a part of his soul flew and searched for a host to attach to. Harry was already fatally injured by then, but Fawkes the phoenix came to his rescue by perching on his arm and shedding some tears. Harry lived on to fight Voldemort on another day, and that bit of his soul which still flew around attached to Fawkes kept him immortal.
While a horcrux would not make a person immortal, a phoenix will reborn whenever it turns to ashes thus they cannot actually die. If part of Harry's soul is going to be within a Phoenix forever, then that could only mean that there is this part of his soul that can never die. This all spells out to this sharp and logical fan theory which says that Harry Potter can indeed be immortal.
This could be a possible explanation as to how Harry came back to life after defeating Voldermort in "The Deathly Hallows." Although this was never confirmed by Rowling and there could be other reasons as why Harry came back to life, this fan theory appears to be the most suitable one.