Listen up, Game of Thrones enthusiasts (read: fellow nerds): Arya Stark is the Prince That Was Promised, and I shall not hear otherwise! (JK, definitely open to other theories, but Arya is looking more and more likely by the episode.)
Quick reminder before we get to Arya: The Prince That Was Promised is the reincarnation of Azor Ahai, a legendary hero chosen by the Lord of Light to fight darkness. A lot of people speculate that either Jon or Daenerys is the Prince That Was Promised due to legend telling us that s/he was “born amidst smoke and salt and would wake dragons out of stone,” etc.—all of which are very Targaryen-like qualities.
But to be honest, there’s plenty of evidence that this prophecy has been about Arya the entire time. Especially after Sunday’s episode… and especially considering what Melisandre said about her forever shutting “brown eyes, blue eyes, green eyes.”
If Arya fulfills Melisandre’s prophecy by offing Daenerys, who has green eyes, she would have killed a representation of both fire (Dany) and ice (the Night King). This is a major piece of evidence that she’s the Prince That Was Promised, considering the prince’s ~song~ is the “song of ice and fire.”
More than that, we know the prince was “born amidst smoke and salt.” And Arya quite literally woke up in a pile of ash and smoke at the end of Sunday’s penultimate episode.