Cassandra de Rolo

Cassandra Johanna Von Musel Klossowski de Rolo is one of Percy's sisters. She is the youngest of seven siblings. As an NPC, she is played by Matthew Mercer.

Excerpt from Percy's Intro
"One day, a mysterious couple, named Lord and Lady Briarwood, came to the court. During a feast held in their honour, the Briarwoods violently took control of the castle, killing or imprisoning everyone who would stand in their way.  Percy awoke chained in the dungeon, only to be freed by his younger sister.  Together, they fled, chased by the Briarwoods' men.  As they ran, Percy's sister took several arrows to the chest and fell."

Archibald Desnay claimed that Cassandra was helping the rebellion.

Cassandra later admitted to collaborating with the Briarwoods so that rebellion would fail.

Trivia

 * Professor Anders cut Cassandra's throat in front of Vax'ildan, it was actually an illusion.
 * Cassandra is the name of a friend of Taliesin in real life, who knows about the show and thinks he's "such a weirdo".