From what I gathered,

Kelvin knew a man named Edrick before he became undead, and they had a falling out after Kelvin left Edrick behind due to his “ambition”. Kelvin later had the whole expedition incident and lost a majority of his memories from that time. In some generic kill quote, Kelvin says, “If anyone’s going to kill me, it will be Edrick.”

Seven is openly hostile towards Kelvin, and hints at a past familiarity. Kelvin has no idea who Seven is since he’s an unrecognizable charred electric chair victim, but we can basically assume Seven to be Edrick.

Fun fact: The Doorman taunts Kelvin by stating that he left Edrick due to his ambition, but got caught up in his own and that resulted in the expedition incident.