Diagram: Grandmaster legendary Feline steel sword is a crafting diagram in Blood and Wine expansion that is needed to craft Grandmaster Legendary Feline steel sword.
This diagram is only available with a New Game +.
This diagram is found along with 2 others (silver sword and gauntlets) during the quest, Scavenger Hunt: Grandmaster Feline Gear, which is started after meeting and talking with Lazare Lafargue about finding grandmaster gear for 5 of the witcher schools.