Grandmaster legendary Feline silver sword is a craftable silver sword and is part of the Cat School Gear in the Blood and Wine expansion with the New Game + option.
One needs all the previous Feline silver sword diagrams to craft the grandmaster version as one of the required crafting components is the legendary Feline silver sword - mastercrafted.
Crafting Requirements 
Min. Required Level: Grandmaster
Notes[]
- This is the only legendary grandmaster rank sword that does not require enriched dimeritium ingots to craft. This is likely an oversight from the developers.