There at least two centuries between theirs lives. Hux - Starkiller - sorcerer who fought star beasts in times before Radahn stopped the stars and become Starscourge Radahn.
Kylo Ren - head of the cavalry at the service of the Fell Omen - disappeared in the underground lands which became the beginning of the Night's Cavalry demise.
One day the Greater Will brings them back and makes them finally meet.