Louis the Younger, sometimes Louis III, was the second eldest of the three sons of Louis II the German and Emma. He succeeded his father as the King of Saxony on 28 August 876 and his elder brother Carloman as King of Bavaria from 880 to 882. He died in 882 and was succeeded in all his territories, which encompassed most of East Francia, by his younger brother, Charles the Fat, already King of Italy and Emperor.
Upon his father's death in 876, Louis fully inherited his subkingdoms, bearing the title rex Francorum ("king of the Franks"). Louis the Younger considered himself the true heir of Louis the German and as his father died in 876, Louis buried him in the abbey of Lorsch, in his own territories, in order to emphasise his primacy to his brothers. Louis also retained his father's chief advisor, Luitbert, Archbishop of Mainz. He and his brother ruled their kingdoms independently but cooperatively and never at war.
Louis fell sick in 881 and died in Frankfurt on 20 January 882. He was buried beside his father in the abbey of Lorsch. By his wife Luitgard of Saxony, he had had a son called Louis (877–879), who died in a fall from a palace window, and a daughter called Hildegard (878–895). Louis had also fathered an illegitimate son, Hugh (855/60 – February 880), either with the daughter of Adalard or with an earlier concubine. Since he left no heir, all his territories fell to his brother Charles, who thus could reunite the entire East Frankish kingdom. Hildegard later joined with the Bavarian magnate Engeldeo in conspiring against King Arnulf and was deprived of her "public honours" in 895, according to the Annals of Fulda.