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SPOILER WARNING: Plot details follow. Caution is advised!
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Aline about Sebastian, A Problem of Memory

Sebastian Verlac was an English Shadowhunter from the London Institute.


In 2016, Sebastian was abducted by Jonathan Christopher Morgenstern. He was brought to New York and kept in Jonathan's closet while the latter took his identity.[1]

For a long time, Jonathan posed as him, and while his family feared that he was dead, they were eventually that he was safe but stayed away from London. Six months after he went missing, his cousin Aline Penhallow came to the New York Institute, where Jonathan was keeping up a charade as him, the charming Englishman who helped Isabelle Lightwood recover from yin fen addiction and advised them how to slay the Greater Demon Azazel. To avoid suspicion, Jonathan demanded that Sebastian tell him everything there is to know about Aline, threatening her life if he didn't. Jonathan then told Aline that he wanted to stay in New York, giving him more time to pose as Sebastian. Shortly after, Sebastian managed to cut away from his restraints and escaped. Before he could approach Aline at the Institute, Jonathan caught up to him and killed him.[2]

Jonathan later brought back his corpse to the apartment he and Valentine were staying at and had abandoned after Jonathan was caught. As a precaution, they left his body with a possessing demon, which Isabelle, Clary, and Jace found. They paid their respects to him after finding him, and killed the demon that had possessed him when it almost attacked them. They promised to make Jonathan pay for what he did to all of them.[3]


Season Two (2B) appearances: 3/20
Mea Maxima Culpa:
Form is only used
You Are Not Your Own:
Form is only used
Those of Demon Blood:
The Fair Folk:
Appears; eclipsed
A Problem of Memory:
Day of Atonement:
Form is only used
A Dark Reflection:
Form is only used
Awake, Arise, or...:
Form is only used
Hail and Farewell:
Appears as a corpse only
Beside Still Water:
Form is only used


  • While posing as Sebastian, Jonathan told Isabelle that he had been addicted to yin fen, which was why he apparently left London—to find his own ways of kicking the addiction—and found his way to New York. He also told her that Sebastian's mother—a stubborn and strong-willed—died when he was young, and that he forgave her despite having made his life miserable.[4] He also claimed to have studied abroad, at the Paris Institute, where he specialized in Greater Demons.[5] Whether there is some truth to this in Sebastian's history is unknown.

The following are elements of the character's book (specifically City of Glass) counterpart that was not adapted or was changed for the series:

  • His book counterpart was from Paris.
  • Sebastian had black hair.
  • The Penhallows had not seen Sebastian in so long that they did not realize that the Sebastian they took in was an impostor; Jonathan only died his hair black to pose as him.