How were Charles Martel and Charlemagne related to each other?
Charles Martel was Charlemagne's son.
Charles Martel and Charlemagne were two names for the same ruler.
Charles Martel was Charlemagne's grandfather.✓Correct answer
Charles Martel was Charlemagne's younger brother.
Explanation
Three generations of one family follow in order here: the victor of the eighth-century battle, then his son who took the royal title, then the grandson who was crowned emperor in the year 800. Reversing the order and making the elder man the younger is the standard slip, and it cannot stand, because the emperor's rule began long after the commander was dead.