The first wife of Andrew II of Hungary, Gertrude played an active role in the political machinations of his early reign. She used her influence to advance her German relatives at court and gifted Hungarian lands to them, angering the Hungarian nobility and inciting them to action. While her husband was off on a military campaign, Gertrude was murdered by a group of discontented nobles. The unsavory affair served as the inspiration for what Hungarian composer's famous opera, Bánk bán?
Source: Gertrude of Merania Killed by Discontented Hungarian Nobles (1213) (http://encyclopedia.thefreedictionary.com/Gertrude+of+Merania)