Who was the prince that was promised?

Ah, that is the great question, isn't it? The television show strongly points towards Jon Snow. His lineage as a Targaryen and a Stark makes him the literal song of ice and fire.

However, in the books, the matter remains beautifully ambiguous. The prophecy's language is very tricky. A compelling case can also be made for Daenerys Targaryen. She was born amidst salt and smoke and woke dragons from stone. Ultimately, George R.R. Martin has left it for us to debate. The true answer is that there is no confirmed answer yet in the source material.