Desire is devoted to Regal and continually works to ensure his success. She believes that Regal's bloodlines are purer than those of his half-brothers, She dislikes Chivalry and Verity because they precede Regal in the line of succession, and similarly dislikes Fitz for the threat he poses to Regal's ascension to the throne.
Desire is overly fond of various intoxicants, which eventually leads to her death.
Desire is frequently rude to Fitz, which makes him anxious to be in her presence or near her chambers.
Desire's death comes some time in the earlier years of Fitz's time at Buckkeep Castle. It is implied that her heavy and prolonged use of several different intoxicants caused her death.