FREDEGUND

'Fredegund' or 'Fredegunda' (also Latin ''Fredegundis'' or French ''Frédégonde''; died 597) was the Queen consort of Chilperic I, the Merovingian Frankish king of Soissons.
Originally a servant, Fredegund became Chilperic's mistress after he had murdered his wife and queen, Galswintha (c. 568). But Galswintha's sister, Brunhilda, in revenge against Chilperic, began a feud which lasted more than 40 years.

Fredegund is said to be responsible for the assassination of Sigebert I in 575 and made attempts on the lives of Guntram (her brother-in-law and the king of Burgundy), Childebert II (Sigebert's son), and Brunhilda.
After the mysterious assassination of Chilperic (584), Fredegund seized his riches and took refuge in the cathedral at Paris. Both she and her surviving son, Clothar II, were protected by Guntram until he died in 592.
Gregory of Tours depicts her as ruthlessly murderous and sadistically cruel; in his account, Fredegund perhaps has few rivals in monstrousness. And although she did not live to see it, her son's execution of Brunhilda bore the mark of Fredegund's hatred: Clothar II had the old queen, now in her sixties, stretched in agony upon the rack for three entire days, then watched her meet her death chained between four horses that were goaded to the four points of the compass, tearing her body asunder.