When Chilperic1 saw this [the marriage of Sigebert2 to the Visigoth princess Brunhild3], although he had already too many wives, he asked for her sister Galswinth, promising through his ambassadors that he would put aside the others if he could only obtain a wife worthy of himself and the daughter of a king. Her father accepted these promises and sent his daughter with much wealth, as he had done before. Now Galswinth was older than Brunhild. And coming to king Chilperic she was received with great honour, and united to him in marriage, and she was also greatly loved by him. For she had brought great treasures. But because of his love of Fredegund whom he had had before, there arose a great scandal which divided them. Galswinth had already been converted to the catholic law and baptised. And complaining to the king that she was continually enduring outrages and had no honour with him, she asked to leave the treasures which she had brought with her and be permitted to go free to her native land. But he made ingenious pretences and calmed her with gentle words. At length he ordered her to be strangled by a slave and found her dead on the bed. After her death God caused a great miracle to appear. For the lighted lamp which hung by a rope in front of her tomb broke the rope without being touched by anyone and dashed on the pavement, and the hard pavement yielded under it and it went down as if into some soft substance and was buried to the middle but not at all damaged. Which seemed a great miracle to all who saw it. But when the king had mourned her death a few days, he married Fredegund again. After this action his brothers thought that the aforementioned queen had been killed at his command, and they expelled him from the kingdom. Chilperic at that time had three sons by his former wife Audovera, namely Theodobert, whom we have mentioned above, Merovech and Clovis.
Gregory of Tours History of the Franks, 4. 28
Translation based on Earnest Brehaut 
1 c. 539 – September 584, King of Neustria
2 c. 535 – c. 575, King of Austrasia (half-brother of Chilperic)
3 c. 540–568, daughter of the Visigoth King Athanagild