I've checked some youtube videos, and it appears to play during the credits.
calls it the Ending Song.
Note: I'm not 100% sure about this, but the evidence points to it. Youtube commenters are referring to an emotional scene that played around the time of this song, and searching for the keywords of that scene returns the ending of the game.
Update: I finished the game. This song does not exactly play during the credits, but it does play at the very end of the main storyline, during the emotional moment I mentioned above. I will not spoil it any further because this moment has significance to people who played earlier installments.