Jillian "Jill" Mastrano Dragomir is a royal moroi and the illegitimate daughter of the late Eric Dragomir and Emily Mastrano, and the half-sister of Lissa and André Dragomir.
She lives with her mother and stepfather in Ann Arbor, Michigan. She attends Vladimir's during school year.
Jill's appearance is typical of Moroi girls: tall, slender, with a small bust and very pale skin. She is not quite six feet tall, but because she is so slim, she appears taller. Jill has long brown hair and very large jade green eyes, the same color as Lissa's. She is initially very clumsy and awkward, but as time goes on, she becomes much more capable and confident, even modeling for a short time.
She is introduced as a gawky, shy girl who is notorious for talking in long strings without taking a breath. She is incredibly innocent and pure of heart. She is also "smart and strong and beautiful," according to Eddie Castile.
Jillian is determined, as she is among a small number of Moroi who want to learn how to fight. She is also loyal to her friends, as she told Christian that Lissa had cheated on him. She is surprisingly mature for her age at times, such as when she agreed to go to the Royal Court in order to give Lissa quorum. Along with this maturity, she is also shown to be wise beyond her years.
A little while after Rose finds out that Jill is Lissa's biological half-sister and the biological daughter of Eric Dragomir, she then appears at her house in Detroit, Michigan, and tells Jill that her stepfather is not her dad. Jill tells her she knows that, and Jill's mother gets very shaky when they are close to telling the truth. Jill then finds out that her father was Eric Dragomir and asks her mom why they didn't tell her. She lets Rose stay the night, but when her stepfather calls guardians on Rose and the gang, she gets kidnapped by Victor Dashkov and his brother. They don't let her sleep because of her ability to be pulled into spirit dreams. Later, Rose, Dimitri, and Sonya find her at a motel with Victor. Sonya goes to get Jill and brings her to the car while the others fight. After Victor Dashkov is killed, she is in a hotel room with Sonya and then goes to the Palace with them. She arrives at court just after Lissa gives her speech, and Rose shocks Lissa as well as the crowd when she announces that Jill is Lissa's half-sister and the illegitimate child of Eric Dragomir. Later, she is seen with Lissa and Rose, where they ask her if she'll be a part of Lissa's coronation ceremony. She is again seen standing next to the throne at the coronation. As she's placing the custom-made crown on Lissa's head, Rose notes that she is dressed in a way that complements Lissa's coronation gown.