Four's Grandfather is only mentioned or seen in flashbacks of Lorien's past. He raised Number Four along with Four's Grandmother and fought against the Mogadorians during the invasion, he ultimately died in battle.
Henri remembers him fondly, telling John that he loved to make people laugh and was always making jokes and pranks with his invisibility Legacy. Four's grandparents complimented each other greatly, his grandfather was carefree while his grandmother was more quiet and made sure everything went to plan behind the scenes.
John remembers that his Grandfather saw him off in the airship that was earth bound, both his grandparents hugged him and made their goodbyes before returning to the battle.
- "Come back to us, you hear? Come back to us." Fours Grandma to Four, in a flashback.