Born: in 629, son of Dagobert I, King d'Austrasie and Ragnetrud d'Austrasie, Some sources assert that Sigebert III was born in the year 631. Note - between 633 and 656: Sigebert III, son of Dagobert and Ragnetrude, was King of Austrasie from 633/634 [at which time he is only 9 to 10 years of age -- Thus, Pepin le Vieux or de Landen truly reigns as the Major Domo] to 656. He reigned under the tutellage of Pepin of Landen [when Pepin de Landen died in 640, Otto succeeded him] and of Grimoald. In 641, the nobles of Austrasia have Otto assassinated and Grimolad, son of Pepin becames Mayor of the Palace, and the Francs lose their sovereignty over Thuringia.
By 643, the Francs would lose all authority over the Allemanians (Germans). Between 644 and 645, after humiliating deafeats against the Thuringians and the Allemanians, Sigebert III, not having any heir, adopts the son of Grimoald and names him Childebert. In 646, Sigebert III's wife gives him a son, Dagobert II, which did not please Grimoald. Ten years later, Sigebert III dies.
He was a very pious man and founder of numerous monasteries. He was placed among the rank of the saints by the Church. Married before 652: Immachilde=Himenechilde, Queen d'Austrasie. Died: on 1 February 656 in France.