This item is a premium Tier 70 Battle Pass reward for Season 2 of the game. In order to obtain the outfit, you must first purchase the Battle Pass Season 2 in the Cash Shop and level it up to level 70. The Black Knight Costume is the final reward of the season 2 Battle Pass. Unfortunately, the outfit is no longer obtainable and is not expected to return.
Black Knight high-quality PNG images with transparent background to use them as you wish (YouTube thumbnails, skin concept and so on).
Used in-game to Shop and Locker, credit to Epic Games.