Grandpa calls his granddaughter's husband granddaughter's husband. The granddaughter is her son's daughter, and she is a direct relative with her grandfather and father. Granddaughter-in-law is the father-in-law of granddaughter-in-law, granddaughter-in-law is the son-in-law of granddaughter-in-law, and granddaughter-in-law has a relationship with her father.

Granddaughter-in-law and grandfather are not related by blood, but by marriage.