Wikipedia
Galswintha (540–568) was the daughter of Athanagild, Visigothic king of Hispania (the Iberian Peninsula, comprising modern Spain and Portugal), and Goiswintha. Galswintha was the sister of Brunhilda, Queen of Austrasia; and the wife of Chilperic I, the Merovingian king of Neustria.
Galswintha and Chilperic were married at Rouen in 567, but soon afterwards she was murdered at the instigation of Chilperic's mistress Fredegund, who then married him. Chilperic in turn was murdered in 584, possibly by Fredegund, but just as likely by someone else, as there were many who had reason to want him killed.
Galswintha's death aroused the enmity of her sister Brunhilda against Chilperic, bringing about 40 years of warfare between the Frankish kingdoms of Austrasia and Neustria.