Saint Elizabeth of Hungary.
From what we know, the Hungarian noblemen had no love lost for Queen Gertrude. They thought that the king was giving her Meranian entourage preferential treatment (even though King András was kind of giving land away to nobles like it was candy), and looked at the foreigners at court with great disdain. Eventually, while King András was off on a campaign in 1213 (it was a pet project, he also participated in a Crusade that failed horribly), a group of Hungarian noblemen, led by the (in)famous Bánk bán, decided to murder the queen.
From what we know, she was stabbed to death - according to some sources, in front of her children. The story was turned into a theater play by Katona József and premiered in 1848. It was made into an opera soon after. The play is mandatory reading in high school, and paints Gertrude as the villain - allegedly she helped her younger brother "seduce" (e.g. rape) Bánk's wife, and she killed herself and her son out of shame. Thus, according to literature, the killing of the queen was justified.
An interesting (and well known) part of the story is a letter: The noblemen asked János, archbishop of Esztergom, for advice as they were planning their deed. The Archbishop, inclined to agree with them but determined to play it safe just in case they failed, composed a letter in Latin:
Reginam occidere nolite timere bonum est si omnes consentiunt ego non contradico
This line, depending on how you read (and punctuate) it, can mean two things:
1. "You don't have to kill the queen, it is good for you to fear, and if all agree, I don't, I'm against it"
2. "Kill the queen, don't fear, it is good, and if all agree, I am not against it."
Punctuation saves lives, people.
(Of course the opera was made into a movie)