ephemeral successor to his father, Theodoric II, as king of Austrasia and Burgundy. Controlled by his great-grandmother Brunhild, he reigned only a matter of weeks before the hostility of the Austrasian nobility, led by Arnulf of Metz (Arnulf of Metz, Saint) and Pippin I, to Brunhild led to his overthrow and the reunification of the Frankish lands under Chlotar II. Both Sigebert and Brunhild were killed by Chlotar.

king of the East Saxons, or Essex (from c. 653), who succeeded Sigebert I. He became a Christian, was baptized (c. 653), and invited such missionaries as Saint Cedd into his land, which became a centre for their work. The date and occasion of Sigebert's death are unknown.