Answer
The answer is Carloman. Pepin the Short ruled Francia jointly with his younger brother Carloman from 741 until Carloman's death in 747, when Pepin became sole ruler. Pepin and Carloman were the sons of Charles Martel, who had been the de facto ruler of Francia but not its king. After their father's death, they inherited his power and continued his successful military campaigns, expanding and consolidating the kingdom.