Sigebert I (sĭg`əbərt), d. 575, Frankish king of Austrasia (561–75), son of Clotaire I. He constantly feuded with his brother Chilperic I Chilperic I (chĭl`pərĭk), d. 584, Frankish king of Neustria (561–84), son of Clotaire I.
..... Click the link for more information. , who had inherited the western portion of the Frankish lands, which came to be known as Neustria. The hatred between the two was intensified after Chilperic murdered (567) his wife, Galswintha, who was the sister of Sigebert's wife, Brunhilda Brunhilda (brənhĭld`ə) or Brunehaut
..... Click the link for more information. . When Chilperic attacked Austrasia in 573, a desire for vengeance made Sigebert vindictive, and in the fighting he overran Neustria. He was about to be proclaimed king of Neustria when he was assassinated by order of Fredegunde Fredegunde (frē'dəgŭn` də), c.545–597, Frankish queen.
..... Click the link for more information. , whom Chilperic had married after Galswintha's death.

Sigebert I

(born 535—died November? 575, Vitry, near Arras) Frankish king of the Merovingian dynasty. On the death of his father, Chlotar I, he became king of Austrasia, and he gained further territory on the death of his brother Charibert I (c. 567). He repelled attacks by the Avars (562, c. 568) and married Brunhild, the daughter of the Visigothic king. Brunhild's sister had married Sigebert's brother Chilperic I and was murdered by him. To avenge his sister-in-law's murder, Sigebert waged civil war against Chilperic, defeating him and taking most of his land. Acclaimed king by his brother's subjects, he was immediately killed by assassins in the service of Fredegund, Chilperic's second wife.